Figure 1: Architectural Model
Copyright ©2003 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark, document use and software licensing rules apply.
This document specifies VoiceXML, the Voice Extensible Markup Language. VoiceXML is designed for creating audio dialogs that feature synthesized speech, digitized audio, recognition of spoken and DTMF key input, recording of spoken input, telephony, and mixed initiative conversations. Its major goal is to bring the advantages of web-based development and content delivery to interactive voice response applications.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. The latest status of this document series is maintained at the W3C.
This is the 28 January 2003 W3C Candidate Recommendation of "Voice Extensible Markup Language (VoiceXML) Version 2.0". W3C publishes a technical report as a Candidate Recommendation to indicate that the document is believed to be stable, and to encourage implementation by the developer community. Candidate Recommendation status is described in section 5.2.3 of the Process Document.
The entrance criteria to the Proposed Recommendation phase is at least two independently developed interoperable implementations of each required feature, and at least one implementation of each feature. Detailed implementation requirements and the invitation for participation in the Implementation Report are provided in the Implementation Report Plan. Note, this specification already has significant implementation experience that will soon be reflected in its Implementation Report. We expect to meet all requirements of that report within a Candidate Recommendation period closing 10th April 2003.
Publication as a Candidate Recommendation does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than "work in progress."
Comments on this document and requests for further information should be sent to the Working Group's public mailing list www-voice@w3.org (archive). Note as a precaution against spam, you should first subscribe to this list by sending an email to <www-voice-request@w3.org> with the word subscribe in the subject line (include the word unsubscribe if you want to unsubscribe). Please check the disposition of comments received during the last call period.
Patent disclosures relevant to this specification may be found on the Working Group's patent disclosure page in conformance with W3C policy.
This document has been produced as part of the W3C Voice Browser Activity, following the procedures set out for the W3C Process. The authors of this document are members of the Voice Browser Working Group (W3C Members only).
A list of current W3C Recommendations and other technical documents can be found at http://www.w3.org/TR/.
In this document, the key words "must", "must not", "required", "shall", "shall not", "should", "should not", "recommended", "may", and "optional" are to be interpreted as described in [RFC2119] and indicate requirement levels for compliant VoiceXML implementations.
This document defines VoiceXML, the Voice Extensible Markup Language. Its background, basic concepts and use are presented in Section 1. The dialog constructs of form, menu and link, and the mechanism (Form Interpretation Algorithm) by which they are interpreted are then introduced in Section 2. User input using DTMF and speech grammars is covered in Section 3, while Section 4 covers system output using speech synthesis and recorded audio. Mechanisms for manipulating dialog control flow, including variables, events, and executable elements, are explained in Section 5. Environment features such as parameters and properties as well as resource handling are specified in Section 6. The appendices provide additional information including the VoiceXML Schema, a detailed specification of the Form Interpretation Algorithm and timing, audio file formats, and statements relating to conformance, internationalization, accessibility and privacy.
The origins of VoiceXML began in 1995 as an XML-based dialog design language intended to simplify the speech recognition application development process within an AT&T project called Phone Markup Language (PML). As AT&T reorganized, teams at AT&T, Lucent and Motorola continued working on their own PML-like languages.
In 1998, W3C hosted a conference on voice browsers. By this time, AT&T and Lucent had different variants of their original PML, while Motorola had developed VoxML, and IBM was developing its own SpeechML. Many other attendees at the conference were also developing similar languages for dialog design; for example, such as HP's TalkML and PipeBeach's VoiceHTML.
The VoiceXML Forum was then formed by AT&T, IBM, Lucent, and Motorola to pool their efforts. The mission of the VoiceXML Forum was to define a standard dialog design language that developers could use to build conversational applications. They chose XML as the basis for this effort because it was clear to them that this was the direction technology was going.
In 2000, the VoiceXML Forum released VoiceXML 1.0 to the public. Shortly thereafter, VoiceXML 1.0 was submitted to the W3C as the basis for the creation of a new international standard. VoiceXML 2.0 is the result of this work based on input from W3C member companies, other W3C working groups, and the public.
Developers familar with VoiceXML 1.0 are particularly directed to Changes from Previous Public Version which summarizes how VoiceXML 2.0 differs from VoiceXML 1.0.
VoiceXML is designed for creating audio dialogs that feature synthesized
speech, digitized audio, recognition of spoken and DTMF key input, recording of
spoken input, telephony, and mixed initiative conversations. Its
major goal is to bring the advantages of web-based development and content
delivery to interactive voice response applications.
Here are two short examples of VoiceXML. The first is the venerable "Hello World":
<?xml version="1.0" encoding="UTF-8"?>
<vxml xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd"
version="2.0">
<form>
<block>Hello World!</block>
</form>
</vxml>
The top-level element is <vxml>, which is mainly a container for dialogs. There are two types of dialogs: forms and menus. Forms present information and gather input; menus offer choices of what to do next. This example has a single form, which contains a block that synthesizes and presents "Hello World!" to the user. Since the form does not specify a successor dialog, the conversation ends.
Our second example asks the user for a choice of drink and then submits it to a server script:
<?xml version="1.0" encoding="UTF-8"?>
<vxml xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd"
version="2.0">
<form>
<field name="drink">
<prompt>Would you like coffee, tea, milk, or nothing?</prompt>
<grammar src="drink.grxml" type="application/srgs+xml"/>
</field>
<block>
<submit next="http://www.drink.example.com/drink2.asp"/>
</block>
</form>
</vxml>
A field is an input field. The user must provide a value for the field before proceeding to the next element in the form. A sample interaction is:
C (computer): Would you like coffee, tea, milk, or nothing?
H (human): Orange juice.
C: I did not understand what you said. (a platform-specific default message.)
C: Would you like coffee, tea, milk, or nothing?
H: Tea
C: (continues in document drink2.asp)
This section contains a high-level architectural model, whose terminology is then used to describe the goals of VoiceXML, its scope, its design principles, and the requirements it places on the systems that support it.
The architectural model assumed by this document has the following components:
Figure 1:
Architectural Model
A document server (e.g. a web server) processes requests from a client application, the VoiceXML Interpreter, through the VoiceXML interpreter context. The server produces VoiceXML documents in reply, which are processed by the VoiceXML Interpreter. The VoiceXML interpreter context may monitor user inputs in parallel with the VoiceXML interpreter. For example, one VoiceXML interpreter context may always listen for a special escape phrase that takes the user to a high-level personal assistant, and another may listen for escape phrases that alter user preferences like volume or text-to-speech characteristics.
The implementation platform is controlled by the VoiceXML interpreter context and by the VoiceXML interpreter. For instance, in an interactive voice response application, the VoiceXML interpreter context may be responsible for detecting an incoming call, acquiring the initial VoiceXML document, and answering the call, while the VoiceXML interpreter conducts the dialog after answer. The implementation platform generates events in response to user actions (e.g. spoken or character input received, disconnect) and system events (e.g. timer expiration). Some of these events are acted upon by the VoiceXML interpreter itself, as specified by the VoiceXML document, while others are acted upon by the VoiceXML interpreter context.
VoiceXML’s main goal is to bring the full power of web development and content delivery to voice response applications, and to free the authors of such applications from low-level programming and resource management. It enables integration of voice services with data services using the familiar client-server paradigm. A voice service is viewed as a sequence of interaction dialogs between a user and an implementation platform. The dialogs are provided by document servers, which may be external to the implementation platform. Document servers maintain overall service logic, perform database and legacy system operations, and produce dialogs. A VoiceXML document specifies each interaction dialog to be conducted by a VoiceXML interpreter. User input affects dialog interpretation and is collected into requests submitted to a document server. The document server replies with another VoiceXML document to continue the user’s session with other dialogs.
VoiceXML is a markup language that:
Minimizes client/server interactions by specifying multiple interactions per document.
Shields application authors from low-level, and platform-specific details.
Separates user interaction code (in VoiceXML) from service logic (e.g. CGI scripts).
Promotes service portability across implementation platforms. VoiceXML is a common language for content providers, tool providers, and platform providers.
Is easy to use for simple interactions, and yet provides language features to support complex dialogs.
While VoiceXML strives to accommodate the requirements of a majority of voice response services, services with stringent requirements may best be served by dedicated applications that employ a finer level of control.
The language describes the human-machine interaction provided by voice response systems, which includes:
Output of synthesized speech (text-to-speech).
Output of audio files.
Recognition of spoken input.
Recognition of DTMF input.
Recording of spoken input.
Control of dialog flow.
Telephony features such as call transfer and disconnect.
The language provides means for collecting character and/or spoken input, assigning the input results to document-defined request variables, and making decisions that affect the interpretation of documents written in the language. A document may be linked to other documents through Universal Resource Identifiers (URIs).
VoiceXML is an XML application [XML].
The language promotes portability of services through abstraction of platform resources.
The language accommodates platform diversity in supported audio file formats, speech grammar formats, and URI schemes. While producers of platforms may support various grammar formats the language requires a common grammar format, namely the XML Form of the W3C Speech Recognition Grammar Specification [SRGS], to facilitate interoperability. Similarly, while various audio formats for playback and recording may be supported, the audio formats described in Appendix E must be supported
The language supports ease of authoring for common types of interactions.
The language has well-defined semantics that preserves the author's intent regarding the behavior of interactions with the user. Client heuristics are not required to determine document element interpretation.
The language recognizes semantic interpretations from grammars and makes this information available to the application.
The language has a control flow mechanism.
The language enables a separation of service logic from interaction behavior.
It is not intended for intensive computation, database operations, or legacy system operations. These are assumed to be handled by resources outside the document interpreter, e.g. a document server.
General service logic, state management, dialog generation, and dialog sequencing are assumed to reside outside the document interpreter.
The language provides ways to link documents using URIs, and also to submit data to server scripts using URIs.
VoiceXML provides ways to identify exactly which data to submit to the server, and which HTTP method (GET or POST) to use in the submittal.
The language does not require document authors to explicitly allocate and deallocate dialog resources, or deal with concurrency. Resource allocation and concurrent threads of control are to be handled by the implementation platform.
This section outlines the requirements on the hardware/software platforms that will support a VoiceXML interpreter.
Document acquisition. The interpreter context is expected to acquire documents for the VoiceXML interpreter to act on. The "http" URI protocol must be supported. In some cases, the document request is generated by the interpretation of a VoiceXML document, while other requests are generated by the interpreter context in response to events outside the scope of the language, for example an incoming phone call. When issuing document requests via http, the interpreter context identifies itself using the "User-Agent" header variable with the value "<name>/<version>", for example, "acme-browser/1.2"
Audio output. An implementation platform must support audio output using audio files and text-to-speech (TTS). The platform must be able to freely sequence TTS and audio output. If an audio output resource is not available, an error.noresource event must be thrown. Audio files are referred to by a URI. The language specifies a required set of audio file formats which must be supported (see Appendix E); additional audio file formats may also be supported.
Audio input. An implementation platform is required to detect and report character and/or spoken input simultaneously and to control input detection interval duration with a timer whose length is specified by a VoiceXML document. If an audio input resource is not available, an error.noresource event must be thrown.
It must report characters (for example, DTMF) entered by a user. Platforms must support the XML form of DTMF grammars described in the W3C Speech Recognition Grammar Specification [SRGS]. They should also support the Augmented BNF (ABNF) form of DTMF grammars described in the W3C Speech Recognition Grammar Specification [SRGS].
It must be able to receive speech recognition grammar data dynamically. It must be able to use speech grammar data in the XML Form of the W3C Speech Recognition Grammar Specification [SRGS]. It should be able to receive speech recognition grammar data in the ABNF form of the W3C Speech Recognition Grammar Specification [SRGS], and may support other formats such as the JSpeech Grammar Format [JSGF] or proprietary formats. Some VoiceXML elements contain speech grammar data; others refer to speech grammar data through a URI. The speech recognizer must be able to accommodate dynamic update of the spoken input for which it is listening through either method of speech grammar data specification.
It must be able to record audio received from the user. The implementation platform must be able to make the recording available to a request variable. The language specifies a required set of recorded audio file formats which must be supported (see Appendix E); additional formats may also be supported.
Transfer The platform should be able to support making a third party connection through a communications network, such as the telephone.
A VoiceXML document (or a set of related documents called an application) forms a conversational finite state machine. The user is always in one conversational state, or dialog, at a time. Each dialog determines the next dialog to transition to. Transitions are specified using URIs, which define the next document and dialog to use. If a URI does not refer to a document, the current document is assumed. If it does not refer to a dialog, the first dialog in the document is assumed. Execution is terminated when a dialog does not specify a successor, or if it has an element that explicitly exits the conversation.
There are two kinds of dialogs: forms and menus. Forms define an interaction that collects values for a set of field item variables. Each field may specify a grammar that defines the allowable inputs for that field. If a form-level grammar is present, it can be used to fill several fields from one utterance. A menu presents the user with a choice of options and then transitions to another dialog based on that choice.
A subdialog is like a function call, in that it provides a mechanism for invoking a new interaction, and returning to the original form. Variable instances, grammars, and state information are saved and are available upon returning to the calling document. Subdialogs can be used, for example, to create a confirmation sequence that may require a database query; to create a set of components that may be shared among documents in a single application; or to create a reusable library of dialogs shared among many applications.
A session begins when the user starts to interact with a VoiceXML interpreter context, continues as documents are loaded and processed, and ends when requested by the user, a document, or the interpreter context.
An application is a set of documents sharing the same application root document. Whenever the user interacts with a document in an application, its application root document is also loaded. The application root document remains loaded while the user is transitioning between other documents in the same application, and it is unloaded when the user transitions to a document that is not in the application. While it is loaded, the application root document's variables are available to the other documents as application variables, and its grammars remain active for the duration of the application, subject to the grammar activation rules discussed in Section 3.1.4.
Figure 2 shows the transition of documents (D) in an application that share a common application root document (root).
Figure 2:
Transitioning between documents in an application.
Each dialog has one or more speech and/or DTMF grammars associated with it. In machine directed applications, each dialog’s grammars are active only when the user is in that dialog. In mixed initiative applications, where the user and the machine alternate in determining what to do next, some of the dialogs are flagged to make their grammars active (i.e., listened for) even when the user is in another dialog in the same document, or on another loaded document in the same application. In this situation, if the user says something matching another dialog’s active grammars, execution transitions to that other dialog, with the user’s utterance treated as if it were said in that dialog. Mixed initiative adds flexibility and power to voice applications.
VoiceXML provides a form-filling mechanism for handling "normal" user input. In addition, VoiceXML defines a mechanism for handling events not covered by the form mechanism.
Events are thrown by the platform under a variety of circumstances, such as when the user does not respond, doesn't respond intelligibly, requests help, etc. The interpreter also throws events if it finds a semantic error in a VoiceXML document. Events are caught by catch elements or their syntactic shorthand. Each element in which an event can occur may specify catch elements. Catch elements are also inherited from enclosing elements "as if by copy". In this way, common event handling behavior can be specified at any level, and it applies to all lower levels.
A link supports mixed initiative. It specifies a grammar that is active whenever the user is in the scope of the link. If user input matches the link’s grammar, control transfers to the link’s destination URI. A link can be used to throw an event or go to a destination URI.
| Element | Purpose | Section |
|---|---|---|
| <assign> | Assign a variable a value | 5.3.2 |
| <audio> | Play an audio clip within a prompt | 4.1.3 |
| <block> | A container of (non-interactive) executable code | 2.3.2 |
| <catch> | Catch an event | 5.2.2 |
| <choice> | Define a menu item | 2.2.2 |
| <clear> | Clear one or more form item variables | 5.3.3 |
| <disconnect> | Disconnect a session | 5.3.11 |
| <else> | Used in <if> elements | 5.3.4 |
| <elseif> | Used in <if> elements | 5.3.4 |
| <enumerate> | Shorthand for enumerating the choices in a menu | 2.2.4 |
| <error> | Catch an error event | 5.2.3 |
| <exit> | Exit a session | 5.3.9 |
| <field> | Declares an input field in a form | 2.3.1 |
| <filled> | An action executed when fields are filled | 2.4 |
| <form> | A dialog for presenting information and collecting data | 2.1 |
| <goto> | Go to another dialog in the same or different document | 5.3.7 |
| <grammar> | Specify a speech recognition or DTMF grammar | 3.1 |
| <help> | Catch a help event | 5.2.3 |
| <if> | Simple conditional logic | 5.3.4 |
| <initial> | Declares initial logic upon entry into a ( mixed initiative ) form | 2.3.3 |
| <link> | Specify a transition common to all dialogs in the link’s scope | 2.5 |
| <log> | Generate a debug message | 5.3.13 |
| <menu> | A dialog for choosing amongst alternative destinations | 2.2.1 |
| <meta> | Define a metadata item as a name/value pair | 6.2.1 |
| <metadata> | Define metadata information using a metadata schema | 6.2.2 |
| <noinput> | Catch a noinput event | 5.2.3 |
| <nomatch> | Catch a nomatch event | 5.2.3 |
| <object> | Interact with a custom extension | 2.3.5 |
| <option> | Specify an option in a <field> | 2.3.1.3 |
| <param> | Parameter in <object> or <subdialog> | 6.4 |
| <prompt> | Queue speech synthesis and audio output to the user | 4.1 |
| <property> | Control implementation platform settings. | 6.3 |
| <record> | Record an audio sample | 2.3.6 |
| <reprompt> | Play a field prompt when a field is re-visited after an event | 5.3.6 |
| <return> | Return from a subdialog. | 5.3.10 |
| <script> | Specify a block of ECMAScript client-side scripting logic | 5.3.12 |
| <subdialog> | Invoke another dialog as a subdialog of the current one | 2.3.4 |
| <submit> | Submit values to a document server | 5.3.8 |
| <throw> | Throw an event. | 5.2.1 |
| <transfer> | Transfer the caller to another destination | 2.3.7 |
| <value> | Insert the value of an expression in a prompt | 4.1.4 |
| <var> | Declare a variable | 5.3.1 |
| <vxml> | Top-level element in each VoiceXML document | 1.5.1 |
A VoiceXML document is primarily composed of top-level elements called dialogs. There are two types of dialogs: forms and menus. A document may also have <meta> and <metadata> elements, <var> and <script> elements, <property> elements, <catch> elements, and <link> elements.
Document execution begins at the first dialog by default. As each dialog executes, it determines the next dialog. When a dialog doesn’t specify a successor dialog, document execution stops.
Here is "Hello World!" expanded to illustrate some of this. It now has a document level variable called "hi" which holds the greeting. Its value is used as the prompt in the first form. Once the first form plays the greeting, it goes to the form named "say_goodbye", which prompts the user with "Goodbye!" Because the second form does not transition to another dialog, it causes the document to be exited.
<?xml version="1.0" encoding="UTF-8"?>
<vxml xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd"
version="2.0">
<meta name="author" content="John Doe"/>
<meta name="maintainer" content="hello-support@hi.example.com"/>
<var name="hi" expr="'Hello World!'"/>
<form>
<block>
<value expr="hi"/>
<goto next="#say_goodbye"/>
</block>
</form>
<form id="say_goodbye">
<block>
Goodbye!
</block>
</form>
</vxml>
Alternatively the forms can be combined:
<?xml version="1.0" encoding="UTF-8"?>
<vxml xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd"
version="2.0">
<meta name="author" content="John Doe"/>
<meta name="maintainer" content="hello-support@hi.example.com"/>
<var name="hi" expr="'Hello World!'"/>
<form>
<block>
<value expr="hi"/> Goodbye!
</block>
</form>
</vxml>
Attributes of <vxml> include:
| version | The version of VoiceXML of this document (required). The current version number is 2.0. |
|---|---|
| xmlns | The designated namespace for VoiceXML (required). The namespace for VoiceXML is defined to be http://www.w3.org/2001/vxml. |
| xml:base | The base URI for this document as defined in [XML-BASE]. As in [HTML], a URI which all relative references within the document take as their base. |
| xml:lang | The language identifier for this document . If omitted, the value is a platform-specific default. |
| application | The URI of this document’s application root document, if any. |
Language information is inherited down the document hierarchy: the value of "xml:lang" is inherited by elements which also define the "xml:lang" attribute, such as <grammar> and <prompt>, unless these elements specify an alternative value.
Normally, each document runs as an isolated application. In cases where you want multiple documents to work together as one application, you select one document to be the application root document, and the rest to be application leaf documents. Each leaf document names the root document in its <vxml> element.
When this is done, every time the interpreter is told to load and execute a leaf document in this application, it first loads the application root document if it is not already loaded. The application root document remains loaded until the interpreter is told to load a document that belongs to a different application. Thus one of the following two conditions always holds during interpretation:
The application root document is loaded and the user is executing in it: there is no leaf document.
The application root document and a single leaf document are both loaded and the user is executing in the leaf document.
If there is a chain of subdialogs defined in separate documents, then there may be more than one leaf document loaded although execution will only be in one of these documents.
When a leaf document load causes a root document load, none of the dialogs in the root document are executed. Execution begins in the leaf document.
There are several benefits to multi-document applications.
Here is a two-document application illustrating this:
Application root document (app-root.vxml)
<?xml version="1.0" encoding="UTF-8"?>
<vxml xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd"
version="2.0">
<var name="bye" expr="'Ciao'"/>
<link next="operator_xfer.vxml">
<grammar type="application/srgs+xml" root="root" version="1.0">
<rule id="root" scope="public">operator</rule>
</grammar>
</link>
</vxml>
Leaf document (leaf.vxml)
<?xml version="1.0" encoding="UTF-8"?>
<vxml xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd"
version="2.0" application="app-root.vxml">
<form id="say_goodbye">
<field name="answer">
<grammar type="application/srgs+xml" src="/grammars/boolean.grxml"/>
<prompt>Shall we say <value expr="application.bye"/>?</prompt>
<filled>
<if cond="answer">
<exit/>
</if>
<clear namelist="answer"/>
</filled>
</field>
</form>
</vxml>
In this example, the application is designed so that leaf.vxml must be loaded first. Its application attribute specifies that app-root.vxml should be used as the application root document. So, app-root.vxml is then loaded, which creates the application variable bye and also defines a link that navigates to operator-xfer.vxml whenever the user says "operator". The user starts out in the say_goodbye form:
C: Shall we say Ciao?
H: Si.
C: I did not understand what you said. (a platform-specific default message.)
C: Shall we say Ciao?
H: Ciao
C: I did not understand what you said.
H: Operator.
C: (Goes to operator_xfer.vxml, which transfers the caller to a human operator.)
Note that when the user is in a multi-document application, at most two documents are loaded at any one time: the application root document and, unless the user is actually interacting with the application root document, an application leaf document. A root document's <vxml> element does not have an application attribute specified. A leaf document's <vxml> element does have an application attribute specified. An interpreter always has an application root document loaded; it does not always have an application leaf document loaded.
The name of the interpreter's current application is the application root document's absolute URI. The absolute URI includes a query string, if present, but it does not include a fragment identifier. The interpreter remains in the same application as long as the name remains the same. When the name changes, a new application is entered and its root context is initialized. The application's root context consists of the variables, grammars, catch elements, scripts, and properties in application scope.
During a user session an interpreter transitions from one document to another as requested by <choice>, <goto> <link>, <subdialog>, and <submit> elements. Some transitions are within an application, others are between applications. The preservation or initialization of the root context depends on the type of transition:
If a document refers to a non-existent application root document, an error.badfetch event is thrown. If a document's application attribute refers to a document that also has an application attribute specified, an error.semantic event is thrown.
The following diagrams illustrate the effect of the transitions between root and leaf documents on the application root context. In these diagrams, boxes represent documents, box texture changes identify root context initialization, solid arrows symbolize transitions to the URI in the arrow's label, dashed vertical arrows indicate an application attribute whose URI is the arrow's label.
Figure 3: Transitions that
Preserve the Root Context
In this diagram, all the documents belong to the same application. The transitions are identified by the numbers 1-4 across the top of the figure. They are:
The next diagram illustrates transitions which initialize the root context.
Figure 4: Transitions that
Initialize the Root Context
A subdialog is a mechanism for decomposing complex sequences of dialogs to better structure them, or to create reusable components. For example, the solicitation of account information may involve gathering several pieces of information, such as account number, and home telephone number. A customer care service might be structured with several independent applications that could share this basic building block, thus it would be reasonable to construct it as a subdialog. This is illustrated in the example below. The first document, app.vxml, seeks to adjust a customer’s account, and in doing so must get the account information and then the adjustment level. The account information is obtained by using a subdialog element that invokes another VoiceXML document to solicit the user input. While the second document is being executed, the calling dialog is suspended, awaiting the return of information. The second document provides the results of its user interactions using a <return> element, and the resulting values are accessed through the variable defined by the name attribute on the <subdialog> element.
Customer Service Application (app.vxml)
<?xml version="1.0" encoding="UTF-8"?>
<vxml xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd"
version="2.0">
<form id="billing_adjustment">
<var name="account_number"/>
<var name="home_phone"/>
<subdialog name="accountinfo" src="acct_info.vxml#basic">
<filled>
<!-- Note the variable defined by "accountinfo" is
returned as an ECMAScript object and it contains two
properties defined by the variables specified in the
"return" element of the subdialog. -->
<assign name="account_number" expr="accountinfo.acctnum"/>
<assign name="home_phone" expr="accountinfo.acctphone"/>
</filled>
</subdialog>
<field name="adjustment_amount">
<grammar type="application/srgs+xml" src="/grammars/currency.grxml"/>
<prompt>
What is the value of your account adjustment?
</prompt>
<filled>
<submit next="/cgi-bin/updateaccount"/>
</filled>
</field>
</form>
</vxml>
Document Containing Account Information Subdialog (acct_info.vxml)
<?xml version="1.0" encoding="UTF-8"?>
<vxml xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd"
version="2.0">
<form id="basic">
<field name="acctnum">
<grammar type="application/srgs+xml" src="/grammars/digits.grxml"/>
<prompt> What is your account number? </prompt>
</field>
<field name="acctphone">
<grammar type="application/srgs+xml" src="/grammars/phone_numbers.grxml"/>
<prompt> What is your home telephone number? </prompt>
<filled>
<!-- The values obtained by the two fields are supplied
to the calling dialog by the "return" element. -->
<return namelist="acctnum acctphone"/>
</filled>
</field>
</form>
</vxml>
Subdialogs add a new execution context when they are invoked.The subdialog could be a new dialog within the existing document, or a new dialog within a new document.
Subdialogs can be composed of several documents. Figure 5 shows the execution flow where a sequence of documents (D) transitions to a subdialog (SD) and then back.
Figure 5: Subdialog
composed of several documents
returning from the last subdialog
document.
The execution context in dialog D2 is suspended when it invokes the subdialog SD1 in document sd1.vxml. This subdialog specifies execution is to be transfered to the dialog in sd2.vxml (using <goto>). Consequently, when the dialog in sd2.vxml returns, control is returned directly to dialog D2.
Figure 6 shows an example of a multi-document subdialog where control is transferred from one subdialog to another.
Figure 6: Subdialog
composed of several documents
returning from the first subdialog
document.
The subdialog in sd1.vxml specifies that control is to be transfered to a second subdialog, SD2, in sd2.vxml. When executing SD2, there are two suspended contexts: the dialog context in D2 is suspending awaiting SD1 to return; and the dialog context in SD1 awaiting SD2 to return. When SD2 returns, control is returned to the SD1. It in turn returns control to dialog D2.
Under certain circumstances (in particular, while the VoiceXML interpreter is processing a disconnect event) the interpreter may continue executing in the final processing state after there is no longer a connection to allow the interpreter to interact with the end user. The purpose of this state is to allow the VoiceXML application to perform any necessary final cleanup, such as submitting information to the application server. For example, the following <catch> element will catch the connection.disconnect.hangup event and execute in the final processing state:
<catch event="connection.disconnect.hangup">
<submit namelist="myExit" next="http://mysite/exit.jsp"/>
</catch>
While in the final processing state the application must remain in the transitioning state and may not enter the waiting state (as described in Section 4.1.8). Thus for example the application should not enter <field>, <record>, or <transfer> while in the final processing state. The VoiceXML interpreter must exit if the VoiceXML application attempts to enter the waiting state while in the final processing state.
Aside from this restriction, execution of the VoiceXML application continues normally while in the final processing state. Thus for example the application may transition between documents while in the final processing state, and the interpreter must exit if no form item is eligible to be selected (as described in Section 2.1.1).
Forms are the key component of VoiceXML documents. A form contains:
A set of form items, elements that are visited in the main loop of the form interpretation algorithm. Form items are subdivided into input items that can be 'filled' by user input and control items that cannot.
Declarations of non-form item variables.
Event handlers.
"Filled" actions, blocks of procedural logic that execute when certain combinations of input item variables are assigned.
Form attributes are:
| id | The name of the form. If specified, the form can be referenced within the document or from another document. For instance <form id="weather">, <goto next="#weather">. |
|---|---|
| scope | The default scope of the form’s grammars. If it is dialog then the form grammars are active only in the form. If the scope is document, then the form grammars are active during any dialog in the same document. If the scope is document and the document is an application root document, then the form grammars are active during any dialog in any document of this application. Note that the scope of individual form grammars takes precedence over the default scope; for example, in non-root documents a form with the default scope "dialog", and a form grammar with the scope "document", then that grammar is active in any dialog in the document. |
This section describes some of the concepts behind forms, and then gives some detailed examples of their operation.
Forms are interpreted by an implicit form interpretation algorithm (FIA). The FIA has a main loop that repeatedly selects a form item and then visits it. The selected form item is the first in document order whose guard condition is not satisfied. For instance, a field’s default guard condition tests to see if the field’s form item variable has a value, so that if a simple form contains only fields, the user will be prompted for each field in turn.
Interpreting a form item generally involves:
Selecting and playing one or more prompts;
Collecting a user input, either a response that fills in one or more input items, or a throwing of some event (help, for instance); and
Interpreting any <filled> actions that pertained to the newly filled in input items.
The FIA ends when it interprets a transfer of control statement (e.g. a <goto> to another dialog or document, or a <submit> of data to the document server). It also ends with an implied <exit> when no form item remains eligible to select.
The FIA is described in more detail in Section 2.1.6.
Form items are the elements that can be visited in the main loop of the form interpretation algorithm. Input items direct the FIA to gather a result for a specific element. When the FIA selects a control item, the control item may contain a block of procedural code to execute, or it may tell the FIA to set up the initial prompt-and-collect for a mixed initiative form.
An input item specifies an input item variable to gather from the user. Input items have prompts to tell the user what to say or key in, grammars that define the allowed inputs, and event handlers that process any resulting events. An input item may also have a <filled> element that defines an action to take just after the input item variable is filled. Input items consist of:
| <field> | An input item whose value is obtained via ASR or DTMF grammars. |
|---|---|
| <record> | An input item whose value is an audio clip recorded by the user. A <record> element could collect a voice mail message, for instance. |
| <transfer> | An input item which transfers the user to another telephone number. If the transfer returns control, the field variable will be set to the result status. |
| <object> | This input item invokes a platform-specific "object" with various parameters. The result of the platform object is an ECMAScript Object. One platform object could be a builtin dialog that gathers credit card information. Another could gather a text message using some proprietary DTMF text entry method. There is no requirement for implementations to provide platform-specific objects, although implementations must handle the <object> element by throwing error.unsupported.objectname if the particular platform-specific object is not supported (more specific error information may be provided in the event "_message" special variable as described in Section 5.2.2.). |
| <subdialog> | A <subdialog> input item is roughly like a function call. It invokes another dialog on the current page, or invokes another VoiceXML document. It returns an ECMAScript Object as its result. |
There are two types of control items:
| <block> | A sequence of procedural statements used for prompting and computation, but not for gathering input. A block has a (normally implicit) form item variable that is set to true just before it is interpreted. |
|---|---|
| <initial> | This element controls the initial interaction in a mixed initiative form. Its prompts should be written to encourage the user to say something matching a form level grammar. When at least one input item variable is filled as a result of recognition during an <initial> element, the form item variable of <initial> becomes true, thus removing it as an alternative for the FIA. |
Each form item has an associated form item variable, which by default is set to undefined when the form is entered. This form item variable will contain the result of interpreting the form item. An input item’s form item variable is also called an input item variable, and it holds the value collected from the user. A form item variable can be given a name using the name attribute, or left nameless, in which case an internal name is generated.
Each form item also has a guard condition, which governs whether or not that form item can be selected by the form interpretation algorithm. The default guard condition just tests to see if the form item variable has a value. If it does, the form item will not be visited.
Typically, input items are given names, but control items are not. Generally form item variables are not given initial values and additional guard conditions are not specified. But sometimes there is a need for more detailed control. One form may have a form item variable initially set to hide a field, and later cleared (e.g., using <clear>) to force the field’s collection. Another field may have a guard condition that activates it only when it has not been collected, and when two other fields have been filled. A block item could execute only when some condition holds true. Thus, fine control can be exercised over the order in which form items are selected and executed by the FIA, however in general, many dialogs can be constructed without resorting to this level of complexity.
In summary, all form items have the following attributes:
| name | The name of a dialog-scoped form item variable that will hold the value of the form item. |
|---|---|
| expr | The initial value of the form item variable; default is ECMAScript undefined. If initialized to a value, then the form item will not be executed unless the form item variable is cleared. |
| cond | An expression to evaluate in conjunction with the test of the form item variable. If absent, this defaults to true, or in the case of <initial>, a test to see if any input item variable has been filled in. |
The simplest and most common type of form is one in which the form items are executed exactly once in sequential order to implement a computer-directed interaction. Here is a weather information service that uses such a form.
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="weather_info">
<block>Welcome to the weather information service.</block>
<field name="state">
<prompt>What state?</prompt>
<grammar src="state.grxml" type="application/srgs+xml"/>
<catch event="help">
Please speak the state for which you want the weather.
</catch>
</field>
<field name="city">
<prompt>What city?</prompt>
<grammar src="city.grxml" type="application/srgs+xml"/>
<catch event="help">
Please speak the city for which you want the weather.
</catch>
</field>
<block>
<submit next="/servlet/weather" namelist="city state"/>
</block>
</form>
</vxml>
This dialog proceeds sequentially:
C (computer): Welcome to the weather information service. What state?
H (human): Help
C: Please speak the state for which you want the weather.
H: Georgia
C: What city?
H: Tblisi
C: I did not understand what you said. What city?
H: Macon
C: The conditions in Macon Georgia are sunny and clear at 11 AM ...
The form interpretation algorithm’s first iteration selects the first block, since its (hidden) form item variable is initially undefined. This block outputs the main prompt, and its form item variable is set to true. On the FIA’s second iteration, the first block is skipped because its form item variable is now defined, and the state field is selected because the dialog variable state is undefined. This field prompts the user for the state, and then sets the variable state to the answer. A detailed description of the filling of form item variables from a field-level grammar may be found in Section 3.1.6. The third form iteration prompts and collects the city field. The fourth iteration executes the final block and transitions to a different URI.
Each field in this example has a prompt to play in order to elicit a response, a grammar that specifies what to listen for, and an event handler for the help event. The help event is thrown whenever the user asks for assistance. The help event handler catches these events and plays a more detailed prompt.
Here is a second directed form, one that prompts for credit card information:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="get_card_info">
<block>We now need your credit card type, number,
and expiration date.</block>
<field name="card_type">
<prompt count="1">What kind of credit card
do you have?</prompt>
<prompt count="2">Type of card?</prompt>
<!-- This is an inline grammar. -->
<grammar type="application/srgs+xml" root="r2" version="1.0">
<rule id="r2" scope="public">
<one-of>
<item>visa</item>
<item>master <item repeat="0-1">card</item></item>
<item>amex</item>
<item>american express</item>
</one-of>
</rule>
</grammar>
<help> Please say Visa, Mastercard, or American Express.</help>
</field>
<field name="card_num">
<grammar type="application/srgs+xml" src="/grammars/digits.grxml"/>
<prompt count="1">What is your card number?</prompt>
<prompt count="2">Card number?</prompt>
<catch event="help">
<if cond="card_type =='amex' || card_type =='american express'">
Please say or key in your 15 digit card number.
<else/>
Please say or key in your 16 digit card number.
</if>
</catch>
<filled>
<if cond="(card_type == 'amex' || card_type =='american express')
&& card_num.length != 15">
American Express card numbers must have 15 digits.
<clear namelist="card_num"/>
<throw event="nomatch"/>
<elseif cond="card_type != 'amex'
&& card_type !='american express'
&& card_num.length != 16"/>
Mastercard and Visa card numbers have 16 digits.
<clear namelist="card_num"/>
<throw event="nomatch"/>
</if>
</filled>
</field>
<field name="expiry_date">
<grammar type="application/srgs+xml" src="/grammars/digits.grxml"/>
<prompt count="1">What is your card's expiration date?</prompt>
<prompt count="2">Expiration date?</prompt>
<help>
Say or key in the expiration date, for example one two oh one.
</help>
<filled>
<!-- validate the mmyy -->
<var name="mm"/>
<var name="i" expr="expiry_date.length"/>
<if cond="i == 3">
<assign name="mm" expr="expiry_date.substring(0,1)"/>
<elseif cond="i == 4"/>
<assign name="mm" expr="expiry_date.substring(0,2)"/>
</if>
<if cond="mm == '' || mm < 1 || mm > 12">
<clear namelist="expiry_date"/>
<throw event="nomatch"/>
</if>
</filled>
</field>
<field name="confirm">
<grammar type="application/srgs+xml" src="/grammars/boolean.grxml"/>
<prompt>
I have <value expr="card_type"/> number
<value expr="card_num"/>, expiring on
<value expr="expiry_date"/>.
Is this correct?
</prompt>
<filled>
<if cond="confirm">
<submit next="place_order.asp"
namelist="card_type card_num expiry_date"/>
</if>
<clear namelist="card_type card_num expiry_date confirm"/>
</filled>
</field>
</form>
</vxml>
Note that the grammar alteratives 'amex' and 'american express' return literal values which need to be handled separately in the conditional expressions. Section 3.1.5 describes how semantic attachments in the grammar can be used to return a single representation of these inputs.
The dialog might go something like this:
C: We now need your credit card type, number, and expiration date.
C: What kind of credit card do you have?
H: Discover
C: I did not understand what you said. (a platform-specific default message.)
C: Type of card? (the second prompt is used now.)
H: Shoot. (fortunately treated as "help" by this platform)
C: Please say Visa, Master card, or American Express.
H: Uh, Amex. (this platform ignores "uh")
C: What is your card number?
H: One two three four ... wait ...
C: I did not understand what you said.
C: Card number?
H: (uses DTMF) 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 #
C: What is your card’s expiration date?
H: one two oh one
C: I have Amex number 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 expiring on 1 2 0 1. Is this correct?
H: Yes
Fields are the major building blocks of forms. A field declares a variable and specifies the prompts, grammars, DTMF sequences, help messages, and other event handlers that are used to obtain it. Each field declares a VoiceXML form item variable in the form’s dialog scope. These may be submitted once the form is filled, or copied into other variables.
Each field has its own speech and/or DTMF grammars, specified explicitly using <grammar> elements, or implicitly using the type attribute. The type attribute is used for builtin grammars, like digits, boolean, or number.
Each field can have one or more prompts. If there is one, it is repeatedly used to prompt the user for the value until one is provided. If there are many, prompts are selected for playback according to the prompt selection algorithm (see Section 4.1.6). The count attribute can be used to determine which prompts to use on each attempt. In the example, prompts become shorter. This is called tapered prompting.
The <catch event="help"> elements are event handlers that define what to do when the user asks for help. Help messages can also be tapered. These can be abbreviated, so that the following two elements are equivalent:
<catch event="help"> Please say visa, mastercard, or amex. </catch> <help> Please say visa, mastercard, or amex. </help>
The <filled> element defines what to do when the user provides a recognized input for that field. One use is to specify integrity constraints over and above the checking done by the grammars, as with the date field above.
The last section talked about forms implementing rigid, computer-directed conversations. To make a form mixed initiative, where both the computer and the human direct the conversation, it must have one or more form-level grammars. The dialog may be written in several ways. One common authoring style combines an <initial> element that prompts for a general response with <field> elements that prompt for specific information. This is illustrated in the example below. More complex techniques, such as using the 'cond' attribute on <field> elements, may achieve a similar effect.
If a form has form-level grammars:
Its input items can be filled in any order.
More than one input item can be filled as a result of a single user utterance.
Only input items (and not control items) can be filled as a result of matching a form-level grammar. The filling of field variables when using a form-level grammar is described in Section 3.1.6.
Also, the form’s grammars can be active when the user is in other dialogs. If a document has two forms on it, say a car rental form and a hotel reservation form, and both forms have grammars that are active for that document, a user could respond to a request for hotel reservation information with information about the car rental, and thus direct the computer to talk about the car rental instead. The user can speak to any active grammar, and have input items set and actions taken in response.
Example. Here is a second version of the weather information service, showing mixed initiative. It has been "enhanced" for illustrative purposes with advertising and with a confirmation of the city and state:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="weather_info">
<grammar src="cityandstate.grxml" type="application/srgs+xml"/>
<!-- Caller can't barge in on today's advertisement. -->
<block>
<prompt bargein="false">
Welcome to the weather information service.
<audio src="http://www.online-ads.example.com/wis.wav"/>
</prompt>
</block>
<initial name="start">
<prompt>
For what city and state would you like the weather?
</prompt>
<help>
Please say the name of the city and
state for which you would like a weather report.
</help>
<!-- If user is silent, reprompt once, then
try directed prompts. -->
<noinput count="1"> <reprompt/></noinput>
<noinput count="2"> <reprompt/>
<assign name="start" expr="true"/></noinput>
</initial>
<field name="state">
<prompt>What state?</prompt>
<help>
Please speak the state for which you want the weather.
</help>
</field>
<field name="city">
<prompt>Please say the city in <value expr="state"/>
for which you want the weather.</prompt>
<help>Please speak the city for which you
want the weather.</help>
<filled>
<!-- Most of our customers are in LA. -->
<if cond="city == 'Los Angeles' && state == undefined">
<assign name="state" expr="'California'"/>
</if>
</filled>
</field>
<field name="go_ahead" modal="true">
<grammar type="application/srgs+xml" src="/grammars/boolean.grxml"/>
<prompt>Do you want to hear the weather for
<value expr="city"/>, <value expr="state"/>?
</prompt>
<filled>
<if cond="go_ahead">
<prompt bargein="false">
<audio src="http://www.online-ads.example.com/wis2.wav"/>
</prompt>
<submit next="/servlet/weather" namelist="city state"/>
</if>
<clear namelist="start city state go_ahead"/>
</filled>
</field>
</form>
</vxml>
Here is a transcript showing the advantages for even a novice user:
C: Welcome to the weather information service. Buy Joe’s Spicy Shrimp Sauce.
C: For what city and state would you like the weather?
H: Uh, California.
C: Please say the city in California for which you want the weather.
H: San Francisco, please.
C: Do you want to hear the weather for San Francisco, California?
H: No
C: For what city and state would you like the weather?
H: Los Angeles.
C: Do you want to hear the weather for Los Angeles, California?
H: Yes
C: Don’t forget, buy Joe’s Spicy Shrimp Sauce tonight!
C: Mostly sunny today with highs in the 80s. Lows tonight from the low 60s ...
The go_ahead field has its modal attribute set to true. This causes all grammars to be disabled except the ones defined in the current form item, so that the only grammar active during this field is the grammar for boolean.
An experienced user can get things done much faster (but is still forced to listen to the ads):
C: Welcome to the weather information service. Buy Joe’s Spicy Shrimp Sauce.
C: What ...
H (barging in): LA
C: Do you ...
H (barging in): Yes
C: Don’t forget, buy Joe’s Spicy Shrimp Sauce tonight!
C: Mostly sunny today with highs in the 80s. Lows tonight from the low 60s ...
The form interpretation algorithm can be customized in several ways. One way is to assign a value to a form item variable, so that its form item will not be selected. Another is to use <clear> to set a form item variable to undefined; this forces the FIA to revisit the form item again.
Another method is to explicitly specify the next form item to visit using <goto nextitem>. This forces an immediate transfer to that form item. No variables, conditions or counters in the targeted form item will be reset. The form item's prompt will be played even if it has already been visited. If the <goto nextitem> occurs in a <filled> action, the rest of the <filled> action and any pending <filled> actions will be skipped.
Here is an example <goto nextitem> executed in response to the exit event:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="survey_2000_03_30">
<catch event="exit">
<reprompt/>
<goto nextitem="confirm_exit"/>
</catch>
<block>
<prompt>
Hello, you have been called at random to answer questions
critical to U.S. foreign policy.
</prompt>
</block>
<field name="q1">
<grammar type="application/srgs+xml" src="/grammars/boolean.grxml"/>
<prompt>Do you agree with the IMF position on
privatizing certain functions of Burkina Faso’s
agriculture ministry?</prompt>
</field>
<field name="q2">
<grammar type="application/srgs+xml" src="/grammars/boolean.grxml"/>
<prompt>If this privatization occurs, will its
effects be beneficial mainly to Ouagadougou and
Bobo-Dioulasso?</prompt>
</field>
<field name="q3">
<grammar type="application/srgs+xml" src="/grammars/boolean.grxml"/>
<prompt>Do you agree that sorghum and millet output
might thereby increase by as much as four percent per
annum?</prompt>
</field>
<block>
<submit next="register" namelist="q1 q2 q3"/>
</block>
<field name="confirm_exit">
<grammar type="application/srgs+xml" src="/grammars/boolean.grxml"/>
<prompt>You have elected to exit. Are you
sure you want to do this, and perhaps adversely affect
U.S. foreign policy vis-a-vis sub-Saharan Africa for
decades to come?</prompt>
<filled>
<if cond="confirm_exit">
Okay, but the U.S. State Department is displeased.
<exit/>
<else/>
Good, let's pick up where we left off.
<clear namelist="confirm_exit"/>
</if>
</filled>
<catch event="noinput nomatch">
<throw event="exit"/>
</catch>
</field>
</form>
</vxml>
If the user says "exit" in response to any of the survey questions, an exit event is thrown by the platform and caught by the <catch> event handler. This handler directs that confirm_exit be the next visited field. The confirm_exit field would not be visited during normal completion of the survey because the preceding <block> element transfers control to the registration script.
We’ve presented the form interpretation algorithm (FIA) at a conceptual level. In this section we describe it in more detail. A more formal description is provided in Appendix C.
Whenever a form is entered, it is initialized. Internal prompt counter variables (in the form’s dialog scope) are reset to 1. Each variable (form-level <var> elements and form item variables) is initialized, in document order, to undefined or to the value of the relevant expr attribute.
The main loop of the FIA has three phases:
The select phase: the next unfilled form item is selected for visiting.
The collect phase: the selected form item is visited, which prompts the user for input, enables the appropriate grammars, and then waits for and collects an input (such as a spoken phrase or DTMF key presses) or an event (such as a request for help or a no input timeout).
The process phase: an input is processed by filling form items and executing <filled> elements to perform actions such as input validation. An event is processed by executing the appropriate event handler for that event type.
Note that the FIA may be given an input (a set of grammar slot/slot value pairs) that was collected while the user was in a different form’s FIA. In this case the first iteration of the main loop skips the select and collect phases, and goes right to the process phase with that input. Also note that if an error occurs in the select or collect phase that causes an event to be generated, the event is thrown and the FIA moves directly into the process phase.
The purpose of the select phase is to select the next form item to visit. This is done as follows:
If a <goto> from the last main loop iteration’s process phase specified a <goto nextitem>, then the specified form item is selected.
Otherwise the first form item whose guard condition is false is chosen to be visited. If an error occurs while checking guard conditions, the event is thrown which skips the collect phase, and is handled in the process phase.
If no guard condition is false, and the last iteration completed the form without encountering an explicit transfer of control, the FIA does an implicit <exit> operation (similarly, if execution proceeds outside of a form, such as when an error is generated outside of a form, and there is no explicit transfer of control, the interpreter will perform an implicit <exit> operation).
The purpose of the collect phase is to collect an input or an event. The selected form item is visited, which performs actions that depend on the type of form item:
If a field item is visited, the FIA selects and queues up any prompts based on the field item’s prompt counter and the prompt conditions. Then it activates and listens for the field level grammar(s) and any active higher-level grammars, and waits for a grammar recognition or for some event.
If a <transfer> is visited, the prompts are queued based on the item’s prompt counter and the prompt conditions. The item grammars are activated. The queue is played before the transfer is executed.
If a <subdialog> or <object> is visited, the prompts are queued based on the item’s prompt counter and the prompt conditions. Grammars are not activated. Instead, the input collection behavior is specified by the executing context for the subdialog or object. The queue is not played before the subdialog or object is executed, but instead should be played during the subsequent input collection.
If an <initial> is visited, the FIA selects and queues up prompts based on the <initial>’s prompt counter and prompt conditions. Then it listens for the form level grammar(s) and any active higher-level grammars. It waits for a grammar recognition or for an event.
A <block> element is visited by setting its form item variable to true, evaluating its content, and then bypassing the process phase. No input is collected, and the next iteration of the FIA’s main loop is entered.
The purpose of the process phase is to process the input or event collected during the previous phases, as follows:
If an input matches a grammar in this form, then:
After completion of the process phase, interpretation continues by returning to the select phase.
A more detailed form interpretation algorithm can be found in Appendix C.
A menu is a convenient syntactic shorthand for a form containing a single anonymous field that prompts the user to make a choice and transitions to different places based on that choice. Like a regular form, it can have its grammar scoped such that it is active when the user is executing another dialog. The following menu offers the user three choices:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<menu>
<prompt>
Welcome home. Say one of: <enumerate/>
</prompt>
<choice next="http://www.sports.example.com/vxml/start.vxml">
Sports
</choice>
<choice next="http://www.weather.example.com/intro.vxml">
Weather
</choice>
<choice next="http://www.stargazer.example.com/voice/astronews.vxml">
Stargazer astrophysics news
</choice>
<noinput>Please say one of <enumerate/></noinput>
</menu>
</vxml>
This dialog might proceed as follows:
C: Welcome home. Say one of: sports; weather; Stargazer astrophysics news.
H: Astrology.
C: I did not understand what you said. (a platform-specific default message.)
C: Welcome home. Say one of: sports; weather; Stargazer astrophysics news.
H: sports.
C: (proceeds to http://www.sports.example.com/vxml/start.vxml)
This identifies the menu, and determines the scope of its grammars. Menu attributes are:
| id | The identifier of the menu. It allows the menu to be the target of a <goto> or a <submit>. |
|---|---|
| scope | The menu’s grammar scope. If it is dialog (the default), the menu’s grammars are only active when the user transitions into the menu. If the scope is document, its grammars are active over the whole document (or if the menu is in the application root document, any loaded document in the application). |
| dtmf | When set to true, the first nine choices that have not explicitly specified a value for the dtmf attribute are given the implicit ones "1", "2", etc. Remaining choices that have not explicitly specified a value for the dtmf attribute will not be assigned DTMF values (and thus cannot be matched via a DTMF keypress). If there are choices which have specified their own DTMF sequences to be something other than "*", "#", or "0", an error.badfetch will be thrown. The default is false. |
| accept | When set to "exact" (the default), the text of the choice elements in the menu defines the exact phrase to be recognized. When set to "approximate", the text of the choice elements defines an approximate recognition phrase (as described under Section 2.2.5). Each <choice> can override this setting. |
The <choice> element serves several purposes:
It may specify a speech grammar, defined either using a <grammar> element or automatically generated by the process described in Section 2.2.5.
It may specify a DTMF grammar, as discussed in Section 2.2.3.
The contents may be used to form the <enumerate> prompt string. This is described in Section 2.2.4.
And it specifies either an event to be thrown or the URI to go to when the choice is selected.
Choice attributes are:
| dtmf | The DTMF sequence for this choice. It is equivalent to a simple DTMF <grammar> and DTMF properties (Section 6.3.3) apply to recognition of the sequence. Unlike DTMF grammars, whitespace is optional: dtmf="123#" is equivalent to dtmf="1 2 3 #". |
|---|---|
| accept | Override the setting for accept in <menu> for this particular choice. When set to "exact" (the default), the text of the choice element defines the exact phrase to be recognized. When set to "approximate", the text of the choice element defines an approximate recognition phrase (as described under Section 2.2.5). |
| next | The URI of next dialog or document. |
| expr | Specify an expression to evaluate as a URI to transition to instead of specifying a next. |
| event | Specify an event to be thrown instead of specifying a next. |
| eventexpr | An ECMAScript expression evaluating to the name of the event to be thrown. |
| message | A message string providing additional context about the event being thrown. The message is available as the value of a variable within the scope of the catch element, see Section 5.2.2. |
| messageexpr | An ECMAScript expression evaluating to the message string. |
| fetchaudio | See Section 6.1. This defaults to the fetchaudio property. |
| fetchhint | See Section 6.1. This defaults to the documentfetchhint property. |
| fetchtimeout | See Section 6.1. This defaults to the fetchtimeout property. |
| maxage | See Section 6.1. This defaults to the documentmaxage property. |
| maxstale | See Section 6.1. This defaults to the documentmaxstale property. |
Exactly one of "next", "expr", "event" or "eventexpr" must be specified; otherwise, an error.badfetch event is thrown. Exactly one of "message" or "messageexpr" may be specified; otherwise, an error.badfetch event is thrown.
If a <grammar> element is specified in <choice>, then the external grammar is used instead of an automatically generated grammar. This allows the developer to precisely control the <choice> grammar; for example:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<menu>
<choice next="http://www.sports.example.com/vxml/start.vxml">
<grammar src="sports.grxml" type="application/srgs+xml"/>
Sports
</choice>
<choice next="http://www.weather.example.com/intro.vxml">
<grammar src="weather.grxml" type="application/srgs+xml"/>
Weather
</choice>
<choice next="http://www.stargazer.example.com/voice/astronews.vxml">
<grammar src="astronews.grxml" type="application/srgs+xml"/>
Stargazer astrophysics
</choice>
</menu>
</vxml>
Menus can rely purely on speech, purely on DTMF, or both in combination by including a <property> element in the <menu>. Here is a DTMF-only menu with explicit DTMF sequences given to each choice, using the choice’s dtmf attribute:
<?xml version="1.0" encoding="UTF-8"?> <vxml version="2.0" xmlns="http://www.w3.org/2001/vxml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.w3.org/2001/vxml http://www.w3.org/TR/voicexml20/vxml.xsd"> <menu> <property name="inputmodes" value="dtmf"/> <prompt> For sports press 1, For weather press 2, For Stargazer astrophysics press 3. </prompt> <choice dtmf="1" next="http://www.sports.example.com/vxml/start.vxml"/> <choice dtmf="2" next="http://www.weather.example.com/intro.vxml"/> <choice dtmf="3" next="http://www.stargazer.example.com/astronews.vxml"/> </menu> </vxml>
Alternatively, you can set the <menu>’s dtmf attribute to true to assign sequential DTMF digits to each of the first nine choices that have not specified their own DTMF sequences: the first choice has DTMF "1", and so on:
<?xml version="1.0" encoding="UTF-8"?> <vxml version="2.0" xmlns="http://www.w3.org/2001/vxml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.w3.org/2001/vxml http://www.w3.org/TR/voicexml20/vxml.xsd"> <menu dtmf="true"> <property name="inputmodes" value="dtmf"/> <prompt> For sports press 1, For weather press 2, For Stargazer astrophysics press 3. </prompt> <choice next="http://www.sports.example.com/vxml/start.vxml"/> <choice next="http://www.weather.example.com/intro.vxml"/> <choice dtmf="0" next="#operator"/> <choice next="http://www.stargazer.example.com/voice/astronews.vxml"/> </menu> </vxml>
The <enumerate> element is an automatically generated description of the choices available to the user. It specifies a template that is applied to each choice in the order they appear in the menu. If it is used with no content, a default template that lists all the choices is used, determined by the interpreter context. If it has content, the content is the template specifier. This specifier may refer to two special variables: _prompt is the choice’s prompt, and _dtmf is the choice’s assigned DTMF sequence. For example, if the menu were rewritten as
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<menu dtmf="true">
<prompt>
Welcome home.
<enumerate>
For <value expr="_prompt"/>, press <value
expr="_dtmf"/>.
</enumerate>
</prompt>
<choice next="http://www.sports.example.com/vxml/start.vxml">
sports </choice>
<choice next="http://www.weather.example.com/intro.vxml">
weather </choice>
<choice next="http://www.stargazer.example.com/voice/astronews.vxml">
Stargazer astrophysics news
</choice>
</menu>
</vxml>
then the menu’s prompt would be:
C: Welcome home. For sports, press 1. For weather, press 2. For Stargazer astrophysics news, press 3.
The <enumerate> element may be used within the prompts and the catch elements associated with <menu> elements and with <field> elements that contain <option> elements, as discussed in Section 2.3.1.3. An error.semantic event is thrown if <enumerate> is used elsewhere (for example, <enumerate> within an <enumerate>).
Any choice phrase specifies a set of words and phrases to listen for. A choice phrase is constructed from the PCDATA of the elements contained directly or indirectly in a <choice> element of a <menu>, or in the <option> element of a <field>.
If the accept attribute is "exact" then the user must say the entire phrase in the same order in which they occur in the choice phrase.
If the accept attribute is "approximate", then the choice may be matched when a user says a subphrase of the expression. For example, in response to the prompt "Stargazer astrophysics news" a user could say "Stargazer", "astrophysics", "Stargazer news", "astrophysics news", and so on. The equivalent grammar may be language and platform dependent.
As an example of using "exact" and "approximate" in different choices, consider this example:
<?xml version="1.0" encoding="UTF-8"?> <vxml version="2.0" xmlns="http://www.w3.org/2001/vxml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.w3.org/2001/vxml http://www.w3.org/TR/voicexml20/vxml.xsd"> <menu accept="approximate"> <choice next="http://www.stargazer.example.com/voice/astronews.vxml"> Stargazer Astrophysics News </choice> <choice accept="exact" next="http://www.physicsweekly.com/voice/example.vxml"> Physics Weekly </choice> <choice accept="exact" next="http://www.particlephysics.com/voice/example.vxml"> Particle Physics Update </choice> <choice next="http://www.astronomytoday.com/voice/example.vxml"> Astronomy Today </choice> </menu> </vxml>
Because "approximate" is specified for the first choice, the user may say a subphrase when matching the first choice; for instance, "Stargazer" or "Astrophysics News". However, because "exact" is specified in the second and third choices, only a complete phrase will match: "Physics Weekly" and "Particle Physics Update".
As an example of the use of PCDATA contained in descendants of the <choice> element, consider the following example:
<choice accept="exact"
next="http://www.stargazer.example.com/voice/astronews.vxml">
<audio src="http://www.stargazer.example.com/space.wav">
Stargazer <emphasis>astrophysics</emphasis> news
</audio>
</choice>
This choice would be read from the audio file, or as "Stargazer Astrophysics News" if the file could not be played. The grammar for the choice would be the exact phrase "Stargazer astrophysics news" gleaned from the PCDATA of the <choice> element’s descendants.
A menu behaves like a form with a single field that does all the work. The menu prompts become field prompts. The menu event handlers become the field event handlers. The menu grammars become form grammars. As with forms, grammar matches in menu will update the application.lastresult$ array. These variables are described in Section 5.1.5. Generated grammars must always produce simple results whose interpretation and utterance values are identical.
Upon entry, the menu’s grammars are built and enabled, and the prompt is played. When the user input matches a choice, control transitions according to the value of the next, expr, event or eventexpr attribute of the <choice>, only one of which may be specified. If an event attribute is specified but its event handler does not cause the interpreter to exit or transition control, then the FIA will clear the form item variable of the menu's anonymous field, causing the menu to be executed again.
A form item is an element of a <form> that can be visited during form interpretation. These elements are <field>, <block>, <initial>, <subdialog>, <object>, <record>, and <transfer>.
All form items have the following characteristics:
They have a result variable, specified by the name attribute. This variable may be given an initial value with the expr attribute.
They have a guard condition specified with the cond attribute. A form item is visited if it is not filled and its cond is not specified or evaluates, after conversion to boolean, to true.
Form items are subdivided into input items, those that define the form’s input item variables, and control items, those that help control the gathering of the form’s input items. Input items (<field>, <subdialog>, <object>, <record>, and <transfer>) generally may contain the following elements:
<filled> elements containing some action to execute after the result input item variable is filled in.
<property> elements to specify properties that are in effect for this input item (the <initial> form item can also contain this element).
<prompt> elements to specify prompts to be played when this element is visited.
<grammar> elements to specify allowable spoken and character input for this input item (<subdialog> and <object> cannot contain this element).
<catch> elements and catch shorthands that are in effect for this input item (the <initial> form item can also contain this element).
Each input item may have an associated set of shadow variables. Shadow variables are used to return results from the execution of an input item, other than the value stored under the name attribute. For example, it may be useful to know the confidence level that was obtained as a result of a recognized grammar in a <field> element. A shadow variable is referenced as name$.shadowvar where name is the value of the field item’s name attribute, and shadowvar is the name of a specific shadow variable. Shadow variables are writeable and can be modified by the application. For example, the <field> element returns a shadow variable confidence. The example below illustrates how this shadow variable is accessed.
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="get_state">
<field name="state">
<prompt> Please say the name of a state. </prompt>
<grammar src="http://mygrammars.example.com/states.gram"
type="application/srgs"/>
<filled>
<if cond="state$.confidence < 0.4">
<throw event="nomatch"/>
</if>
</filled>
</field>
</form>
</vxml>
In the example, the confidence of the result is examined, and the result is rejected if the confidence is too low.
A field specifies an input item to be gathered from the user. Attributes of fields are:
| name | The form item variable in the dialog scope that will hold the result. The name must be unique among form items in the form. If the name is not unique, then a badfetch error is thrown when the document is fetched. The name must conform to the variable naming conventions in Section 5.1. |
|---|---|
| expr | The initial value of the form item variable; default is ECMAScript undefined. If initialized to a value, then the form item will not be visited unless the form item variable is cleared. |
| cond | An expression that must evaluate to true after conversion to boolean in order for the form item to be visited. The form item can also be visited if the attribute is not specified. |
| type | The type of field, i.e., the name of a builtin grammar type (see Appendix P). Platform support for builtin grammar types is optional. If the specified builtin type is not supported by the platform, an error.unsupported.builtin event is thrown. |
| slot | The name of the grammar slot used to populate the variable (if it is absent, it defaults to the variable name). This attribute is useful in the case where the grammar format being used has a mechanism for returning sets of slot/value pairs and the slot names differ from the form item variable names. |
| modal | If this is false (the default) all active grammars are turned on while collecting this field. If this is true, then only the field’s grammars are enabled: all others are temporarily disabled. |
The shadow variables of a <field> element with the name name are given in Table 10. The values of the utterance, inputmode and interpretation shadow variables must be the same as those in application.lastresult$ (see Section 5.1.5).
| name$.utterance | The raw string of words that were recognized. The exact tokenization and spelling is platform-specific (e.g. "five hundred thirty" or "5 hundred 30" or even "530"). In the case of a DTMF grammar, this variable will contain the matched digit string. |
|---|---|
| name$.inputmode | The mode in which user input was provided: dtmf or voice. |
| name$.interpretation | An ECMAscript variable containing the interpretation as described in Section 3.1.5. |
| name$.confidence |
The confidence level for the name field and may range from 0.0-1.0. A value of 0.0 indicates minimum confidence, and a value of 1.0 indicates maximum confidence. A platform may use the utterance confidence (the value of application.lastresult$.confidence) as the value of name$.confidence. This distinction between field and utterance level confidence is platform-dependent. More specific interpretation of a confidence value is platform-dependent since its computation is likely to differ between platforms. |
Explicit grammars can be specified via a URI, which can be absolute or relative:
<field name="flavor">
<prompt>What is your favorite ice cream?</prompt>
<grammar src="../grammars/ice_cream.grxml"
type="application/srgs+xml"/>
</field>
Grammars can be specified inline, for example using a W3C ABNF grammar:
<field name="flavor"> <prompt>What is your favorite flavor?</prompt> <help>Say one of vanilla, chocolate, or strawberry.</help> <grammar mode="voice" type="application/srgs"> #ABNF 1.0; $options = vanilla | chocolate | strawberry </grammar> </field>
If both the <grammar> src attribute and an inline grammar are specified, then an error.badfetch is thrown.
Platform support for builtin resources such as speech grammars, DTMF grammars and audio files is optional. These resources are accessed using platform-specific URIs, such as "http://localhost:5000/grammar/boolean", or platform-specific schemes such as the commonly used 'builtin' scheme, "builtin:grammar/boolean".
If a platform supports access to builtin resources, then it should support access to fundamental builtin grammars (see Appendix P); for example
<grammar src="builtin:grammar/boolean"/> <grammar src="builtin:dtmf/boolean"/>
where the first <grammar> references the builtin boolean speech grammar, and the second references the builtin boolean DTMF grammar.
By definition the following:
<field type="sample"> <prompt>Prompt for builtin grammar</prompt> </field>
is equivalent to the following platform-specific builtin grammars :
<field> <grammar src="builtin:grammar/sample"/> <grammar src="builtin:dtmf/sample"/> <prompt>Prompt for builtin grammar</prompt> </field>
where sample is one of the fundamental builtin field types (e.g., boolean, date, etc.).
In addition, platform-specific builtin URI schemes may be used to access grammars that are supported by particular interpreter contexts. It is recommended that plaform-specific builtin grammar names begin with the string "x-", as this namespace will not be used in future versions of the standard.
Examples of platform-specific builtin grammars:
<grammar src="builtin:grammar/x-sample"/> <grammar src="builtin:dtmf/x-sample"/>
When a simple set of alternatives is all that is needed to specify the legal input values for a field, it may be more convenient to use an option list than a grammar. An option list is represented by a set of <option> elements contained in a <field> element. Each <option> element contains PCDATA that is used to generate a speech grammar. This follows the grammar generation method described for <choice> in Section 2.2.5 . Attributes may be used to specify a DTMF sequence for each option and to control the value assigned to the field's form item variable. When an option is chosen, the value attribute determines the interpretation value for the field's shadow variable and for application.lastresult$.
The following field offers the user three choices and assigns the value of the value attribute of the selected option to the maincourse variable:
<field name="maincourse">
<prompt>
Please select an entree. Today, we are featuring <enumerate/>
</prompt>
<option dtmf="1" value="fish"> swordfish </option>
<option dtmf="2" value="beef"> roast beef </option>
<option dtmf="3" value="chicken"> frog legs </option>
<filled>
<submit next="/cgi-bin/maincourse.cgi"
method="post" namelist="maincourse"/>
</filled>
</field>
This conversation might sound like:
C: Please select an entree. Today, we’re featuring swordfish; roast beef; frog legs.
H: frog legs
C: (assigns "chicken" to "maincourse", then submits "maincourse=chicken" to /maincourse.cgi)
The following example shows proper and improper use of <enumerate> in a catch element of a form with several fields containing <option> elements:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form>
<block>
We need a few more details to complete your order.
</block>
<field name="color">
<prompt>Which color?</prompt>
<option>red</option>
<option>blue</option>
<option>green</option>
</field>
<field name="size">
<prompt>Which size?</prompt>
<option>small</option>
<option>medium</option>
<option>large</option>
</field>
<field name="quantity">
<grammar type="application/srgs+xml" src="/grammars/number.grxml"/>
<prompt>How many?</prompt>
</field>
<block>
Thank you. Your order is being processed.
<submit next="details.cgi" namelist="color size quantity"/>
</block>
<catch event="help nomatch">
Your options are <enumerate/>.
</catch>
</form>
</vxml>
A scenario might be:
C: We need a few more details to complete your order. Which color?
H: help. (throws "help" event caught by form-level <catch>)
C: Your options are red, blue, green.
H: red.
C: Which size?
H: 7 (throws "nomatch" event caught by form-level <catch>)
C: Your options are small, medium, large.
H: small.
In the steps above, the <enumerate/> in the form-level catch had something to enumerate: the <option> elements in the "color" and "size" <field> elements. The next <field>, however, is different:
C: How many?
H: a lot. (throws "nomatch" event caught by form-level <catch>)
The form-level <catch>'s use of <enumerate> causes an "error.semantic" event to be thrown because the "quantity" <field> does not contain any <option> elements that can be enumerated.
One solution is to add a field-level <catch> to the "quantity" <field>:
<catch event="help nomatch">
Please say the number of items to be ordered.
</catch>
The "nomatch" event would then be caught locally, resulting in the following possible completion of the scenario:
C: Please say the number of items to be ordered.
H: 50
C: Thank you. Your order is being processed.
The <enumerate> element is also discussed in Section 2.2.4.
The attributes of <option> are:
| dtmf | The DTMF sequence for this option. It is equivalent to a simple DTMF <grammar> and DTMF properties (Section 6.3.3) apply to recognition of the sequence. Unlike DTMF grammars, whitespace is optional: dtmf="123#" is equivalent to dtmf="1 2 3 #". |
|---|---|
| accept | When set to "exact" (the default), the text of the option element defines the exact phrase to be recognized. When set to "approximate", the text of the option element defines an approximate recognition phrase (as described in Section 2.2.5). |
| value | The string to assign to the field’s form item variable when a user selects this option, whether by speech or DTMF. The default assignment is the CDATA content of the <option> element with leading and trailing white space removed. If this does not exist, then the DTMF sequence is used instead. |
The use of <option> does not preclude the simultaneous use of <grammar>. The result would be the match from either 'grammar', not unlike the occurence of two <grammar> elements in the same <field> representing a disjunction of choices.
This element is a form item. It contains executable content that is executed if the block’s form item variable is undefined and the block's cond attribute, if any, evaluates to true.
<block> Welcome to Flamingo, your source for lawn ornaments. </block>
The form item variable is automatically set to true just before the block is entered. Therefore, blocks are typically executed just once per form invocation.
Sometimes you may need more control over blocks. To do this, you can name the form item variable, and set or clear it to control execution of the <block>. This variable is declared in the dialog scope of the form.
Attributes of <block> include:
| name | The name of the form item variable used to track whether this block is eligible to be executed; defaults to an inaccessible internal variable. |
|---|---|
| expr | The initial value of the form item variable; default is ECMAScript undefined. If initialized to a value, then the form item will not be visited unless the form item variable is cleared. |
| cond | An expression that must evaluate to true after conversion to boolean in order for the form item to be visited. |
In a typical mixed initiative form, an <initial> element is visited when the user is initially being prompted for form-wide information, and has not yet entered into the directed mode where each field is visited individually. Like field items, it has prompts, catches, and event counters. Unlike field items, <initial> has no grammars, and no <filled> action. For instance:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="get_from_and_to_cities">
<grammar src="http://www.directions.example.com/grammars/from_to.grxml"
type="application/srgs+xml"/>
<block>
Welcome to the Driving Directions By Phone.
</block>
<initial name="bypass_init">
<prompt>
Where do you want to drive from and to?
</prompt>
<nomatch count="1">
Please say something like "from Atlanta Georgia to Toledo Ohio".
</nomatch>
<nomatch count="2">
I'm sorry, I still don't understand.
I'll ask you for information one piece at a time.
<assign name="bypass_init" expr="true"/>
<reprompt/>
</nomatch>
</initial>
<field name="from_city">
<grammar src="http://www.directions.example.com/grammars/city.grxml"
type="application/srgs+xml"/>
<prompt>From which city are you leaving?</prompt>
</field>
<field name="to_city">
<grammar src="http://www.directions.example.com/grammars/city.grxml"
type="application/srgs+xml"/>
<prompt>Which city are you going to?</prompt>
</field>
</form>
</vxml>
If an event occurs while visiting an <initial>, then one of its event handlers executes. As with other form items, <initial> continues to be eligible to be visited while its form item variable is undefined and while its cond attribute is true. If one or more of the field item variables is set by user input, then all <initial> form item variables are set to true, before any <filled> actions are executed.
An <initial> form item variable can be manipulated explicitly to disable, or re-enable the <initial>'s eligibility to the FIA. For example, in the program above, the <initial>'s form item variable is set on the second nomatch event. This causes the FIA to no longer consider the <initial> and to choose the next form item, which is a <field> to prompt explicitly for the origination city. Similarly, an <initial>’s form item variable could be cleared, so that <initial> gets selected again by the FIA.
More than one <initial> may be specified in the same form. When the form is entered only the first <initial> in document order that is eligible according to its cond attribute will be visited. After the first form item variable is filled, all <initial> form item variables are set to true so that they are not visited. Explicitly clearing the <initial>s can allow them to be reused, and even allow a different <initial> to be selected on subsequent iterations of the FIA.
The cond attribute can also be used to select which <initial> to use in a given iteration. An application could provide multiple <initial>s but mark them for use only under special circumstances by using their cond attribute; for example, if the cond attribute were used to test for novice versus advanced operation mode, and only use the <initial>s in advanced mode. Furthermore, if the first <initial> in document order specified a value for its cond attribute which was never fulfilled, then it would never be executed. If all <initial>s had cond values which prevented their selection, then none would be executed.
Normal grammar scoping rules apply when visiting an <initial>, as described in Section 3.1.3.. In particular, no grammars scoped to a <field> are active.
Note: explicit assignment of values to input item variables does not affect the value of an <initial>’s form item variable.
Attributes of <initial> include:
| name | The name of a form item variable used to track whether the <initial> is eligible to execute; defaults to an inaccessible internal variable. |
|---|---|
| expr | The initial value of the form item variable; default is ECMAScript undefined. If initialized to a value, then the form item will not be visited unless the form item variable is cleared. |
| cond | An expression that must evaluate to true after conversion to boolean in order for the form item to be visited. |
Subdialogs are a mechanism for reusing common dialogs and building libraries of reusable applications.
The <subdialog> element invokes a 'called' dialog (known as the subdialog) identified by its src or srcexpr attribute in the 'calling' dialog. The subdialog executes in a new execution context that includes all the declarations and state information for the subdialog, the subdialog’s document, and the subdialog’s application root (if present), with counters reset, and variables initialized. The subdialog proceeds until the execution of a <return> or <exit> element, or until no form items remain eligible for the FIA to select (equivalent to an <exit>). A <return> element causes control and data to be returned to the calling dialog (Section 5.3.10). When the subdialog returns, its execution context is deleted, and execution resumes in the calling dialog with any appropriate <filled> elements.
The subdialog context and the context of the called dialog are independent, even if the dialogs are in the same document. Variables in the scope chain of the calling dialog are not shared with the called subdialog: there is no sharing of variable instances between execution contexts. Even when the subdialog is specified in the same document as the calling dialog, its execution context contains different variable instances. When the subdialog and calling dialog are in different documents but share a root document, the subdialog's root variables are likewise different instances. All variable bindings applied in the subdialog context are lost on return to the calling context.
Within the subdialog context, however, normal scoping rules for grammars, events and variables apply. Active grammars in a subdialog include default grammars defined by the interpreter context and appropriately scoped grammars in <link>, <menu> and <form> elements in the subdialog's document and its root document. Event handling and variable binding likewise follow the standard scoping hierarchy.
From a programming perspective, subdialogs behave differently from subroutines because the calling and called contexts are independent. While a subroutine can access variable instances in its calling routine, a subdialog cannot access the same variable instance defined in its calling dialog. Similarly, subdialogs do not follow the event percolation model in languages like Java where an event thrown in a method automatically percolates up to the calling context if not handled in the called context. Events thrown in a subdialog are treated by event handlers defined within its context; they can only be passed to the calling context by a local event handler which explicitly returns the event to the calling context (see Section 5.3.10).
The subdialog is specified by the URI reference in the <subdialog>'s src or srcexpr attribute (see [RFC2396]). If this URI reference contains an absolute or relative URI, which may include a query string, then that URI is fetched and the subdialog is found in the resulting document. If the <subdialog> has a namelist attribute, then those variables are added to the query string of the URI.
If the URI reference contains only a fragment (i.e., no absolute or relative URI), and if there is no namelist attribute, then there is no fetch: the subdialog is found in the current document.
The URI reference's fragment, if any, specifies the subdialog to invoke. When there is no fragment, the subdialog invoked is the lexically first dialog in the document.
If the URI reference is not valid (i.e. the dialog or document does not exist), an error.badfetch must be thrown. Note that for errors which occur during a dialog or document transition, the scope in which errors are handled is platform specific.
The attributes are:
| name | The result returned from the subdialog, an ECMAScript object whose properties are the ones defined in the namelist attribute of the <return> element. |
|---|---|
| expr | The initial value of the form item variable; default is ECMAScript undefined. If initialized to a value, then the form item will not be visited unless the form item variable is cleared. |
| cond | An expression that must evaluate to true after conversion to boolean in order for the form item to be visited. |
| namelist | The list of variables to submit. The default is to submit no variables. If a namelist is supplied, it may contain individual variable references which are submitted with the same qualification used in the namelist. Declared VoiceXML and ECMAScript variables can be referenced. |
| src | The URI of the subdialog. |
| srcexpr | An ECMAScript expression yielding the URI of the subdialog |
| method | See Section 5.3.8. |
| enctype | See Section 5.3.8. |
| fetchaudio | See Section 6.1. This defaults to the fetchaudio property. |
| fetchtimeout | See Section 6.1. This defaults to the fetchtimeout property. |
| fetchhint | See Section 6.1. This defaults to the documentfetchhint property |
| maxage | See Section 6.1. This defaults to the documentmaxage property. |
| maxstale | See Section 6.1. This defaults to the documentmaxstale property. |
Exactly one of "src" or "srcexpr" must be specified; otherwise, an error.badfetch event is thrown.
The <subdialog> element may contain elements common to all form items, and may also contain <param> elements. The <param> elements of a <subdialog> specify the parameters to pass to the subdialog. These parameters must be declared in the subdialog using <var> elements; it is a semantic error to attempt to set a form item variable or an undeclared variable using <param>. When a subdialog initializes, its variables are initialized in document order to the value specified by the <param> element with the corresponding name. The parameter values are computed by evaluating the <param> expr attribute in the context of the <param> element. An expr attribute in the <var> element is ignored in this case. If no corresponding <param> is specified to <var> element, an expr attribute is used as a default value, or the variable is undefined if the expr attribute is unspecified as with the regular <form> element.
In the example below, the birthday of an individual is used to validate their driver's license. The src attribute of the subdialog refers to a form that is within the same document. The <param> element is used to pass the birthday value to the subdialog.
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<!-- form dialog that calls a subdialog -->
<form>
<subdialog name="result" src="#getdriverslicense">
<param name="birthday" expr="'2000-02-10'"/>
<filled>
<submit next="http://myservice.example.com/cgi-bin/process"/>
</filled>
</subdialog>
</form>
<!-- subdialog to get drivers license -->
<form id="getdriverslicense">
<var name="birthday"/>
<field name="drivelicense">
<grammar src="http://grammarlib/drivegrammar.grxml"
type="application/srgs+xml"/>
<prompt> Please say your drivers license number. </prompt>
<filled>
<if cond="validdrivelicense(drivelicense,birthday)">
<var name="status" expr="true"/>
<else/>
<var name="status" expr="false"/>
</if>
<return namelist="drivelicense status"/>
</filled>
</field>
</form>
</vxml>
The driver’s license value is returned to calling dialog, along with a status variable in order to indicate whether the license is valid or not.
This example also illustrates the convenience of using <param> as a means for forwarding data to the subdialog as a means of instantiating values in the subdialog without using server side scripting. An alternate solution that uses scripting, is shown below.
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form>
<field name="birthday">
<grammar type="application/srgs+xml" src="/grammars/date.grxml"/>
What is your birthday?
</field>
<subdialog name="result"
src="/cgi-bin/getlib#getdriverslicense"
namelist="birthday">
<filled>
<submit next="http://myservice.example.com/cgi-bin/process"/>
</filled>
</subdialog>
</form>
</vxml>
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="getdriverslicense">
<var name="birthday" expr="'1980-02-10'"/>
<!-- Generated by server script -->
<field name="drivelicense">
<grammar src="http://grammarlib/drivegrammar.grxml"
type="application/srgs+xml"/>
<prompt>
Please say your drivers license number.
</prompt>
<filled>
<if cond="validdrivelicense(drivelicense,birthday)">
<var name="status" expr="true"/>
<else/>
<var name="status" expr="false"/>
</if>
<return namelist="drivelicense status"/>
</filled>
</field>
</form>
</vxml>
In the above example, a server side script had to generate the document and embed the birthday value.
One last example is shown below that illustrates a subdialog to capture general credit card information. First the subdialog is defined in a separate document; it is intended to be reusable across different applications. It returns a status, the credit card number, and the expiry date; if a result cannot be obtained, the status is returned with value "no_result".
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<!-- Example of subdialog to collect credit card information. -->
<!-- file is at http://www.somedomain.example.com/ccn.vxml -->
<form id="getcredit">
<var name="status" expr="'no_result'"/>
<field name="creditcardnum">
<prompt>
What is your credit card number?
</prompt>
<help>
I am trying to collect your credit card information.
<reprompt/>
</help>
<nomatch>
<return namelist="status"/>
</nomatch>
<grammar src="ccn.grxml" type="application/srgs+xml"/>
</field>
<field name="expirydate">
<grammar type="application/srgs+xml" src="/grammars/date.grxml"/>
<prompt>
What is the expiry date of this card?
</prompt>
<help>
I am trying to collect the expiry date of the credit
card number you provided.
<reprompt/>
</help>
<nomatch>
<return namelist="status"/>
</nomatch>
</field>
<block>
<assign name="status" expr="'result'"/>
<return namelist="status creditcardnum expirydate"/>
</block>
</form>
</vxml>
An application that includes a calling dialog is shown below. It obtains the name of a software product and operating system using a mixed initiative dialog, and then solicits credit card information using the subdialog.
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<!-- Example main program -->
<!-- http://www.somedomain.example.com/main.vxml -->
<!-- calls subdialog ccn.vxml -->
<!-- assume this gets defined by some dialog -->
<var name="username"/>
<form id="buysoftware">
<var name="ccn"/>
<var name="exp"/>
<grammar src="buysoftware.grxml" type="application/srgs+xml"/>
<initial name="start">
<prompt>
Please tell us the software product you wish to buy
and the operating system on which it must run.
</prompt>
<noinput>
<assign name="start" expr="true"/>
</noinput>
</initial>
<field name="product">
<prompt>
Which software product would you like to buy?
</prompt>
</field>
<field name="operatingsystem">
<prompt>
Which operating system does this software need to run on?
</prompt>
</field>
<subdialog name="cc_results"
src="http://somedomain.example.com/ccn.vxml">
<filled>
<if cond="cc_results.status=='no_result'">
Sorry, your credit card information could not be
Obtained. This order is cancelled.
<exit/>
<else/>
<assign name="ccn" expr="cc_results.creditcardnum"/>
<assign name="exp" expr="cc_results.expirydate"/>
</if>
</filled>
</subdialog>
<block>
We will now process your order. Please hold.
<submit next="www.somedomain.example.com/process_order.asp"
namelist="username product operatingsystem ccn exp"/>
</block>
</form>
</vxml>
A VoiceXML implementation platform may expose platform-specific functionality for use by a VoiceXML application via the <object> element. The <object> element makes direct use of its own content during initialization (e.g. <param> child element) and execution. As a result, <object> content cannot be treated as alternative content. Notice that like other field items, <object> has prompts and catch elements. It may also have <filled> actions.
For example, a platform-specifc credit card collection object could be accessed like this:
<object
name="debit"
classid="method://credit_card/gather_and_debit"
data="http://www.recordings.example.com/prompts/credit/jesse.jar">
<param name="amount" expr="document.amt"/>
<param name="vendor" expr="vendor_num"/>
</object>
In this example, the <param> element (Section 6.4) is used to pass parameters to the object when it is invoked. When this <object> is executed, it returns an ECMAScript object as the value of its form item variable. This <block> presents the values returned from the credit card object:
<block>
<prompt>
The card type is <value expr="debit.card"/>.
</prompt>
<prompt>
The card number is <value expr="debit.card_no"/>.
</prompt>
<prompt>
The expiration date is <value expr="debit.expiry_date"/>.
</prompt>
<prompt>
The approval code is <value expr="debit.approval_code"/>.
</prompt>
<prompt>The confirmation number is
<value expr="debit.conf_no"/>.
</prompt>
</block>
As another example, suppose that a platform has a feature that allows the user to enter arbitrary text messages using a telephone keypad.
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="gather_pager_message">
<object name="message"
classid="builtin://keypad_text_input">
<prompt>
Enter your message by pressing your keypad once
per letter. For a space, enter star. To end the
message, press the pound sign.
</prompt>
</object>
<block>
<assign name="document.pager_message" expr="message.text"/>
<goto next="#confirm_pager_message"/>
</block>
</form>
</vxml>
The user is first prompted for the pager message, then keys it in. The <block> copies the message to the variable document.pager_message.
Attributes of <object> include:
| name | When the object is evaluated, it sets this variable to an ECMAScript value whose type is defined by the object. |
|---|---|
| expr | The initial value of the form item variable; default is ECMAScript undefined. If initialized to a value, then the form item will not be visited unless the form item variable is cleared. |
| cond | An expression that must evaluate to true after conversion to boolean in order for the form item to be visited. |
| classid | The URI specifying the location of the object’s implementation. The URI conventions are platform-dependent. |
| codebase | The base path used to resolve relative URIs specified by classid, data, and archive. It defaults to the base URI of the current document. |
| codetype | The content type of data expected when downloading the object specified by classid. When absent it defaults to the value of the type attribute. |
| data | The URI specifying the location of the object’s data. If it is a relative URI, it is interpreted relative to the codebase attribute. |
| type | The content type of the data specified by the data attribute. |
| archive | A space-separated list of URIs for archives containing resources
relevant to the object, which may include the resources specified by the
classid and data attributes. URIs which are relative are interpreted
relative to the codebase attribute. |
| fetchhint | See Section 6.1. This defaults to the objectfetchhint property. |
| fetchtimeout | See Section 6.1. This defaults to the fetchtimeout property. |
| maxage | See Section 6.1. This defaults to the objectmaxage property. |
| maxstale | See Section 6.1. This defaults to the objectmaxstale property. |
There is no requirement for implementations to provide platform-specific objects, although implementations must handle the <object> element by throwing error.unsupported.objectname if the particular platform-specific object is not supported. If an implementation does this, it is considered to be supporting the <object> element.
The object itself is responsible for determining whether parameter names or values it receives are invalid. If so, the <object> element throws an error. The error may be either object-specific or one of the standard errors listed in Section 5.2.6.
The <record> element is an input item that collects a recording from the user. A reference to the recorded audio is stored in the input item variable, which can be played back (using the expr attribute on <audio>) or submitted to a server, as shown in this example:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form>
<property name="bargein" value="true"/>
<block>
<prompt>
Riley is not available to take your call.
</prompt>
</block>
<record name="msg" beep="true" maxtime="10s"
finalsilence="4000ms" dtmfterm="true" type="audio/x-wav">
<prompt timeout="5s">
Record a message after the beep.
</prompt>
<noinput>
I didn't hear anything, please try again.
</noinput>
</record>
<field name="confirm">
<grammar type="application/srgs+xml" src="/grammars/boolean.grxml"/>
<prompt>
Your message is <audio expr="msg"/>.
</prompt>
<prompt>
To keep it, say yes. To discard it, say no.
</prompt>
<filled>
<if cond="confirm">
<submit next="save_message.pl" enctype="multipart/form-data"
method="post" namelist="msg"/>
</if>
<clear/>
</filled>
</field>
</form>
</vxml>
The user is prompted to record a message, and then records it. The recording terminates when one of the following conditions is met: the interval of final silence occurs, a DTMF key is pressed, the maximum recording time is exceeded, or the caller hangs up. The recording is played back, and if the user approves it, is sent on to the server for storage using the HTTP POST method. Notice that like other input items, <record> has grammar, prompt and catch elements. It may also have <filled> actions.
Figure 7: Timing
of prompts, audio recording, and DTMF input
When a user hangs up during recording, the recording terminates and a connection.disconnect.hangup event is thrown. However, audio recorded up until the hangup is available through the <record> variable. Applications, such as simple voicemail services, can then return audio data to a server even after disconnection:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form>
<record name="msg" beep="true" maxtime="10s"
finalsilence="4000ms" dtmfterm="true" type="audio/x-wav">
<prompt timeout="5s">
Record a message after the beep.
</prompt>
<noinput>
I didn't hear anything, please try again.
</noinput>
<catch event="connection.disconnect.hangup">
<submit next="./voicemail_server.asp"/>
</catch>
</record>
</form>
</vxml>
A recording begins at the earliest after the playback of any prompts (including the 'beep' tone if defined). As an optimization, a platform may begin recording when the user starts speaking.
A timeout interval is defined to begin immediately after prompt playback (including the 'beep' tone if defined) and its duration is determined by the 'timeout' property. If the timeout interval is exceeded before recording begins, then a <noinput> event is thrown.
A maxtime interval is defined to begin when recording begins and its duration is determined by a 'maxtime' attribute. If the maxtime interval is exceeded before recording ends, then the recording is terminated and the maxtime shadow variable is set to 'true'.
A recording ends when an event is thrown, DTMF or speech input matches an active grammar, or the maxtime interval is exceeded. As an optimization, a platform may end recording after a silence interval (set by the 'finalsilence' attribute) indicating the user has stopped speaking.
If no audio is collected during execution of <record>, then the record variable remains unfilled (note). This can occur, for example, when DTMF or speech input is received during prompt playback or the timeout interval (if the developer wants input during prompt playback to initiate recording, then prompts should be placed in an immediately preceding <field> with a zero timeout).
The <record> element contains a 'dtmfterm' attribute as a developer convenience. A 'dtmfterm' attribute with the value 'true' is equivalent to the definition of a local DTMF grammar which matches any DTMF input.
Any DTMF keypress matching an active grammar terminates recording. DTMF keypresses not matching an active grammar are ignored (and therefore do not terminate or otherwise affect recording) and may optionally be removed from the signal by the platform.
Platform support for recognition of speech grammars during recording is optional. If the platform supports simultaneous recognition and recording, then spoken input matching an active grammar terminates recording. The 'terminating' speech input is accessible via application.lastresult$ and the item's utterance and confidence shadow variables. The audio of the recognized 'terminating' speech input is not available and is not part of the recording.
If the termination grammar matched (DTMF or speech) is a local grammar, the recording is placed in the record variable. Otherwise, the record variable is left unfilled (note) and the form interpretation algorithm is invoked. In each case, application.lastresult$ and the item's shadow variables are assigned.
note Although the record variable is not filled with a recording in this case, a match of a non-local grammar may nevertheless result in an assignment of some value to the record variable (see Section 3.1.6).
The attributes of <record> are:
| name |
The input item variable that will hold the recording. Note that how this variable is implemented may vary between platforms (although all platforms must support its behaviour in <audio> and <submit> as described in this specification). |
|---|---|
| expr | The initial value of the form item variable; default is ECMAScript undefined. If initialized to a value, then the form item will not be visited unless the form item variable is cleared. |
| cond | An expression that must evaluate to true after conversion to boolean in order for the form item to be visited. |
| modal | If this is true (the default) all non-local speech and DTMF grammars are not active while making the recording. If this is false, non-local speech and DTMF grammars are active. |
| beep | If true, a tone is emitted just prior to recording. Defaults to false. |
| maxtime | The maximum duration to record. The value is a Time Designation (see Section 6.5). Defaults to a platform-specific value. |
| finalsilence | The interval of silence that indicates end of speech. The value is a Time Designation (see Section 6.5). Defaults to a platform-specific value. |
| dtmfterm | If true, any DTMF keypress not matched by an active grammar will be treated as a match of an active (anonymous) local DTMF grammar. Defaults to true. |
| type | The media format of the resulting recording. Platforms must support the audio file formats specified in Appendix E (other formats may also be supported). Defaults to a platform-specific format which should be one of the required formats. |
The <record> element has the following shadow variables set after the recording has been made:
| name$.duration | The duration of the recording in milliseconds. |
|---|---|
| name$.size | The size of the recording in bytes. |
| name$.termchar | If the dtmfterm attribute is true, and the user terminates the recording by pressing a DTMF key, then this shadow variable is the key pressed (e.g. "#"). Otherwise it is undefined. |
| name$.maxtime | Boolean, true if the recording was terminated because the maxtime duration was reached. |
| name$.utterance | The string of words used if recording was terminated by speech recognition input; otherwise it is undefined. |
| name$.confidence | The confidence level (0.0 - 1.0) for the utterance if the recording is terminated by speech recognition input; otherwise, it is undefined. |
The <transfer> element directs the interpreter to connect the caller to another entity (e.g. telephone line or another voice application). During the transfer operation, the current interpreter session is suspended.
There are a variety of ways an implementation platform can initiate a transfer, including "bridge", "blind", network-based redirect (sometimes referred to as "take back and transfer"), "switchhook transfer", etc. Bridge and blind transfer types are supported; the others are highly dependent upon specific platform and network features and configuration and therefore are outside the scope of this specification.
The <transfer> element is optional, though platforms should support it. Platforms that support <transfer> may support bridge or blind transfer types, or both. Platforms that support bridge transfer may optionally support DTMF, speech recognition, or both, during the call transfer to drop the far-end.
Attributes are:
| name | Stores the outcome of a bridge transfer attempt. In the case of a blind transfer, this variable is undefined. | ||||
|---|---|---|---|---|---|
| expr | The initial value of the form item variable; default is ECMAScript undefined. If initialized to a value, then the form item will not be visited unless the form item variable is cleared. | ||||
| cond | An expression that must evaluate to true in order for the form item to be visited. | ||||
| dest | The URI of the destination (telephone, IP telephony address). Platforms must support the tel: URL syntax described in [RFC2806] and may support other URI-based addressing schemes. | ||||
| destexpr | An ECMAScript expression yielding the URI of the destination. | ||||
| bridge |
Determines whether the platform remains in the connection with the caller and callee.
| ||||
| connecttimeout | The time to wait while trying to connect the call before returning the noanswer condition. The value is a Time Designation (see Section 6.5). Only applies if bridge is true. Default is platform specific. | ||||
| maxtime | The time that the call is allowed to last, or 0s if no limit is imposed. The value is a Time Designation (see Section 6.5). Only applies if bridge is true. Default is 0s. | ||||
| transferaudio |
The URI of audio source to play while the transfer attempt is in progress (before far-end answer). If the resource cannot be fetched, the error is ignored and the transfer continues; what the caller hears is platform-dependent. | ||||
| aai |
Application-to-application information. A string containing data sent to an application on the far-end, available in the session variable session.connection.aai. The transmission of aai data may depend upon signaling network gateways and data translation (e.g. ISDN to SIP); the status of data sent to a remote site is not known or reported. Although all platforms must support the aai attribute, platforms are not required to send aai data and need not support receipt of aai data. Platforms that cannot receive aai data must set the session.connection.aai variable to the ECMAscript undefined value. The underlying transmission mechanism may impose data length limits. | ||||
| aaiexpr |
An ECMAScript expression yielding the AAI data. |
Exactly one of "dest" or "destexpr" may be specified; otherwise, an error.badfetch event is thrown. Likewise, exactly one of "aai" or "aaiexpr" may be specified; otherwise, an error.badfetch event is thrown.
With a blind transfer, an attempt is made to connect the original caller with the callee. Any prompts preceeding the <transfer>, as well as prompts within the <transfer>, are queued and played before the transfer attempt begins; bargein properties apply as normal.
Figure 8: Audio Connections
during a blind transfer: <transfer bridge="false">
Any audio source specified by the transferaudio attribute is ignored since no audio can be played from the platform to the caller during the transfer attempt. Whether the connection is successful or not, the implementation platform cannot regain control of the connections.
Connection status is not available. For example, it is not possible to know whether the callee was busy, when a successful call ends, etc. However, some error conditions may be reported if known to the platform, such as if the caller is not authorized to call the destination, or if the destination URI is malformed.
Once the transfer begins and the interpreter disconnects from the session, the platform throws connection.disconnect.transfer and document interpretation continues normally.
Any connection between the caller and callee remains in place regardless of document execution.
| Action | Value of form item variable |
Event or Error | Reason |
|---|---|---|---|
| transfer begins | undefined | connection.disconnect.transfer | An attempt has been made to transfer the caller to another line and will not return. |
| transfer ends | unknown | The transfer ended but the reason is not known. |
For a bridge transfer, the platform connects the caller to the callee in a full duplex conversation.
Figure 9: Audio Connections
during a bridge transfer: <transfer bridge="true">
Any prompts preceeding the <transfer>, as well as prompts within the <transfer>, are queued and played before the transfer attempt begins. The bargein control applies normally. Specification of bargeintype is ignored; "hotword" is set by default.
Platforms may optionally support listening for caller commands to terminate the transfer by specifying one or more grammars inside the <transfer> element. The <transfer> element is modal in that no grammar defined outside its scope is active. The platform will monitor during playing of prompts and during the entire length of the transfer connecting and talking phases:
A successful match will terminate the transfer (the connection to the callee); document interpretation continues normally. An unsuccessful match is ignored. If no grammars are specified, the platform will not listen to input from the caller.
The platform does not monitor in-band signals or voice input from the callee.
While attempting to connect to the callee, the platform monitors call progress indicators (in-band and/or out-of-band, depending upon the particular connection type and protocols). For the duration of a successful transfer, the platform monitors for (out-of-band) telephony events, such as disconnect, on both call legs.
If the callee disconnects, the caller resumes his session with the interpreter. If the caller disconnects, the platform disconnects the callee, and document interpretation continues normally. If both the caller and callee are disconnected by the network, document interpretation continues normally.
The possible outcomes for a bridge transfer before the connection to the callee is established are:
| Action | Value of form item variable |
Event | Reason |
|---|---|---|---|
| caller disconnects | connection.disconnect.hangup | The caller hung up. | |
| caller disconnects callee | near_end_disconnect | The caller forced the callee to disconnect via a DTMF or voice command. | |
| callee busy | busy | The callee was busy. | |
| network busy | network_busy | An intermediate network refused the call. | |
| callee does not answer | noanswer | There was no answer within the time specified by the connecttimeout attribute. | |
| --- | unknown | The transfer ended but the reason is not known. |
The possible outcomes for a bridge transfer after the connection to the callee is established are:
| Action | Value of form item variable |
Event | Reason |
|---|---|---|---|
| caller disconnects | connection.disconnect.hangup | The caller hung up. | |
| caller disconnects | near_end_disconnect | The caller forced the callee to disconnect via a DTMF or voice command. | |
| platform disconnects callee | maxtime_disconnect |
The callee was disconnected by the platform because the call duration reached the value of maxtime attribute. | |
| network disconnects callee | network_disconnect |
The network disconnected the callee from the platform. | |
| callee disconnects | far_end_disconnect | The callee hung up. | |
| --- | unknown | The transfer ended but the reason is not known. |
If the caller disconnects by hanging up (either during a call transfer or call transfer attempt), the connection to the callee (if one exists) is dropped, a connection.disconnect.hangup event will be thrown, and dialog execution will transition to a handler for the hangup event (if one exists). The form item variable, and thus shadow variables, will not be set.
If execution of <transfer> continues normally, then its form item variable is set, and the following shadow variables will be set:
| name$.duration |
The duration of a call transfer in seconds. The duration is 0 if a call attempt was terminated by the caller (using a voice or DTMF command) prior to being answered. |
|---|---|
| name$.inputmode | The input mode of the terminating command (dtmf or voice). |
| name$.utterance | The utterance text used if transfer was terminated by speech recognition input or the DTMF result if the transfer was terminated by DTMF input; otherwise it is undefined. |
If the transfer was terminated by speech recognition input, then application.lastresult$ is assigned as usual.
During a bridge transfer, it might be desirable to play audio to the caller while the platform attempts to connect to the callee. For example, an advertisement ("Buy Joe's Spicy Shrimp Sauce") or informational message ("Your call is very important to us; please wait while we connect you to the next available agent.") might be provided in place of call progress information (ringing, busy, network announcements, etc.).
At the point the outgoing call begins, audio specified by transferaudio begins playing. Playing of transferaudio terminates when the answer status of the far-end connection is determined. This status isn't always known, since the far-end switch can play audio (such as a Special Information Tone, busy tone, network busy tone, or a recording saying the connection can't be made) with out actually "answering" the call.
If a specified audio file play duration is shorter than the time it takes to connect the far-end, the caller may hear silence, platform-specific audio, or call progress information, depending upon the platform.
One of the following events may be thrown during a transfer:
| Event | Reason | Transfer type |
|---|---|---|
| connection.disconnect.hangup | The caller hung up. | bridge |
| connection.disconnect.transfer | An attempt has been made to transfer the caller to another line and will not return. | blind |
If a transfer attempt could not be made, one of the following errors will be thrown:
| Error | Reason | Transfer type |
|---|---|---|
|
The caller is not allowed to call the destination. | blind and bridge |
|
The destination URI is malformed. | blind and bridge |
|
The platform is not able to place a call to the destination. | bridge |
|
The platform cannot allocate resources to place the call. | bridge |
|
The protocol stack for this connection raised an exception that does not correspond to one of the other error.connection events. | bridge |
|
The platform does not support blind transfer. | blind |
| error.unsupported.transfer.bridge | The platform does not support bridge transfer. | bridge |
|
The platform does not support the URI format used. The special variable _message (Section 5.2.2) will contain the string "The URI x is not a supported URI format" where x is the URI from the dest or destexpr <transfer> attributes. | blind and bridge |
The following example attempts to perform a bridge transfer the caller to a another party, and wait for that conversation to terminate. Prompts may be included before or within the <transfer> element. This may be used to inform the caller of what is happening, with a notice such as "Please wait while we transfer your call." The <prompt> within the <block>, and the <prompt> within <transfer> are queued and played before actually performing the transfer. After the audio queue is flushed, the outgoing call is initiated. By default, the caller is connected to the outgoing telephony channel. The "transferaudio" attribute specifies an audio file to be played to the caller in place of audio from the far-end until the far-end answers. If the audio source is longer than the connect time, the audio will stop playing immediately upon far-end answer.
Figure 10: Sequence and
timing during an example of a bridge transfer
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="xfer">
<var name="mydur" expr="0"/>
<block>
<!-- queued and played before starting the transfer -->
<prompt>
Calling Riley. Please wait.
</prompt>
</block>
<!-- Play music while attempting to connect to far-end -->
<!-- "hotword" bargeintype during transferaudio only -->
<!-- Wait up to 60 seconds for the far end to answer -->
<transfer name="mycall" dest="tel:+1-555-123-4567"
transferaudio="music.wav" connecttimeout="60s" bridge="true">
<!-- queued and played before starting the transfer -->
<!-- bargein properties apply during this prompt -->
<prompt>
Say cancel to disconnect this call at any time.
</prompt>
<!-- specify an external grammar to listen for "cancel" command -->
<grammar src="cancel.grxml" type="application/srgs+xml"/>
<filled>
<assign name="mydur" expr="mycall$.duration"/>
<if cond="mycall == 'busy'">
<prompt>
Riley's line is busy. Please call again later.
</prompt>
<elseif cond="mycall == 'noanswer'"/>
<prompt>
Riley can't answer the phone now. Please call
again later.
</prompt>
</if>
</filled>
</transfer>
<!-- submit call statistics to server -->
<block>
<submit namelist="mycall mydur" next="/cgi-bin/report"/>
</block>
</form>
</vxml>
The <filled> element specifies an action to perform when some combination of input items are filled. It may occur in two places: as a child of the <form> element, or as a child of an input item.
As a child of a <form> element, the <filled> element can be used to perform actions that occur when a combination of one or more input items is filled. For example, the following <filled> element does a cross-check to ensure that a starting city field differs from the ending city field:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="get_starting_and_ending_cities">
<field name="start_city">
<grammar src="http://www.grammars.example.com/voicexml/city.grxml"
type="application/srgs+xml"/>
<prompt>What is the starting city?</prompt>
</field>
<field name="end_city">
<grammar src="http://www.grammars.example.com/voicexml/city.grxml"
type="application/srgs+xml"/>
<prompt>What is the ending city?</prompt>
</field>
<filled mode="all" namelist="start_city end_city">
<if cond="start_city == end_city">
<prompt>
You can't fly from and to the same city.
</prompt>
<clear/>
</if>
</filled>
</form>
</vxml>
If the <filled> element appears inside an input item, it specifies an action to perform after that input item is filled in:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="get_city">
<field name="city">
<grammar type="application/srgs+xml"
src="http://www.ship-it.example.com/grammars/served_cities.grxml"/>
<prompt>What is the city?</prompt>
<filled>
<if cond="city == 'Novosibirsk'">
<prompt>
Note, Novosibirsk service ends next year.
</prompt>
</if>
</filled>
</field>
</form>
</vxml>
After each gathering of the user’s input, all the input items mentioned in the input are set, and then the interpreter looks at each <filled> element in document order (no preference is given to ones in input items vs. ones in the form). Those whose conditions are matched by the utterance are then executed in order, until there are no more, or until one transfers control or throws an event.
Attributes include:
| mode | Either all (the default), or any. If any, this action is executed when any of the specified input items is filled by the last user input. If all, this action is executed when all of the mentioned input items are filled, and at least one has been filled by the last user input. A <filled> element in an input item cannot specify a mode. |
|---|---|
| namelist | The input items to trigger on. For a <filled> in a form, namelist defaults to the names (explicit and implicit) of the form’s input items. A <filled> element in an input item cannot specify a namelist; the namelist in this case is the input item name. Note that control items are not permitted in this list. |
A <link> element may have one or more grammars which are scoped to the element containing the <link>. A "scope" attribute on the element containing the <link> has no effect on the scope of the <link> grammars (for example, when a <link> is contained in a <form> with scope="document", the <link> grammars are scoped to the form, not to the document). Grammar elements contained in the <link> are not permitted to specify scope. When one of these grammars is matched, the link activates, and either:
Transitions to a new document or dialog (like <goto>), or
Throws an event (like <throw>).
For instance, this link activates when you say "books" or press "2".
<link next="http://www.voicexml.org/books/main.vxml">
<grammar mode="voice" version="1.0" root="root">
<rule id="root" scope="public">
<one-of>
<item>books</item>
<item>VoiceXML books</item>
</one-of>
</rule>
</grammar>
<grammar mode="dtmf" version="1.0" root="r2">
<rule id="r2" scope="public"> 2 </rule>
</grammar>
</link>
This link takes you to a dynamically determined dialog in the current document:
<link expr="'#' + document.helpstate">
<grammar mode="voice" version="1.0" root="root">
<rule id="root" scope="public"> help </rule>
</grammar>
</link>
The <link> element can be a child of <vxml>, <form>, or of the form items <field> and <initial>. A link at the <vxml> level has grammars that are active throughout the document. A link at the <form> level has grammars active while the user is in that form. If an application root document has a document-level link, its grammars are active no matter what document of the application is being executed.
If execution is in a modal form item, then link grammars at the form or document level are not active.
You can also define a link that, when matched, throws an event instead of going to a new document. This event is thrown at the current location in the execution, not at the location where the link is specified. For example, if the user matches this link’s grammar or enters '2' on the keypad, a help event is thrown in the form item the user was visiting and is handled by the best qualified <catch> in the item's scope (see Section 5.2.4 for further details):
<link dtmf="2" event="help">
<grammar mode="voice" version="1.0" root="r5">
<rule id="r5" scope="public">
<one-of>
<item>arrgh</item>
<item>alas all is lost</item>
<item>fie ye froward machine</item>
<item>I don't get it</item>
</one-of>
</rule>
</grammar>
</link>
When a link is matched, application.lastresult$ is assigned. This allows callflow decisions to be made downstream based on the actual semantic result. An example appears in Section 5.1.5.
Conceptually the link element can be thought of as having two parts: condition and action. The "condition" is the content of the link element, i.e. the grammar(s) that must be matched in order for the link to be activated. The "action" is specified by the attributes of the element, i.e. where to transition or which event to throw. The "condition" is resolved/evaluated lexically, while the "action" is resolved/evaluated dynamically. Specifically this means that
Attributes of <link> are:
| next | The URI to go to. This URI is a document (perhaps with an anchor to specify the starting dialog), or a dialog in the current document (just a bare anchor). |
|---|---|
| expr | Like next, except that the URI is dynamically determined by evaluating the given ECMAScript expression. |
| event | The event to throw when the user matches one of the link grammars. |
| eventexpr | An ECMAScript expression evaluating to the name of the event to throw when the user matches one of the link grammars. |
| message | A message string providing additional context about the event being thrown. The message is available as the value of a variable within the scope of the catch element, see Section 5.2.2. |
| messageexpr | An ECMAScript expression evaluating to the message string. |
| dtmf | The DTMF sequence for this link. It is equivalent to a simple DTMF <grammar> and DTMF properties (Section 6.3.3) apply to recognition of the sequence. Unlike DTMF grammars, whitespace is optional: dtmf="123#" is equivalent to dtmf="1 2 3 #". The attribute can be used at the same time as other <grammar>s: the link is activated when user input matches a link grammar or the DTMF sequence. |
| fetchaudio | See Section 6.1. This defaults to the fetchaudio property. |
| fetchhint | See Section 6.1. This defaults to the documentfetchhint property. |
| fetchtimeout | See Section 6.1. This defaults to the fetchtimeout property. |
| maxage | See Section 6.1. This defaults to the documentmaxage property. |
| maxstale | See Section 6.1. This defaults to the documentmaxstale property. |
Exactly one of "next", "expr", "event" or "eventexpr" must be specified; otherwise, an error.badfetch event is thrown. Exactly one of "message" or "messageexpr" may be specified; otherwise, an error.badfetch event is thrown.
The <grammar> element is used to provide a speech grammar that
specifies a set of utterances that a user may speak to perform an action or supply information, and
for a matching utterance, returns a corresponding semantic interpretation. This may be a simple value (such as a string), a flat set of attribute-value pairs (such as day, month, and year), or a nested object (for a complex request).
The <grammar> element is designed to accommodate any grammar format that meets these two requirements. VoiceXML platforms must support at least one common format, the XML Form of the W3C Speech Recognition Grammar Specification [SRGS]. VoiceXML platforms should support the Augmented BNF (ABNF) Form of the W3C Speech Recognition Grammar Specification [SRGS]. VoiceXML platforms may choose to support grammar formats other than SRGS. For instance, a platform might use the <grammar> element's support for PCDATA to inline a proprietary grammar definition or use the "src" and "type" attributes for an external one.
VoiceXML platforms must be a Conforming XML Form Grammar Processor as defined in the W3C Speech Recognition Grammar Specification [SRGS]. While this requires a platform to process documents with one or more "xml:lang" attributes defined, it does not require that the platform must be multi-lingual. When an unsupported language is encountered, the platform throws an error.unsupported.language event which specifies the unsupported language in its message variable.
The following elements are defined in the XML Form of the W3C Speech Recognition Grammar Specification [SRGS] and are available in VoiceXML 2.0. This document does not redefine these elements. Refer to the W3C Speech Recognition Grammar Specification [SRGS] for definitions and examples.
| Element | Purpose | Section (in [SRGS]) |
|---|---|---|
| <grammar> | Root element of an XML grammar | 4. |
| <meta> | Header declaration of meta content of an HTTP equivalent | 4.11.1 |
| <metadata> | Header declaration of XML metadata content | 4.11.2 |
| <lexicon> | Header declaration of a pronunciation lexicon | 4.10 |
| <rule> | Declare a named rule expansion of a grammar | 3. |
| <token> | Define a word or other entity that may serve as input | 2.1 |
| <ruleref> | Refer to a rule defined locally or externally | 2.2 |
| <item> | Define an expansion with optional repeating and probability | 2.3 |
| <one-of> | Define a set of alternative rule expansions | 2.4 |
| <example> | Element contained within a rule definition that provides an example of input that matches the rule | 3.3 |
| <tag> | Define an arbitrary string that to be included inline in an expansion which may be used for semantic interpretation | 2.6 |
The <grammar> element may be used to specify an inline grammar or an external grammar. An inline grammar is specified by the content of a <grammar> element and defines an entire grammar:
<grammar type="media-type" mode="voice">
inline speech grammar
</grammar>
It may be necessary in this case to enclose the content in a CDATA section [XML]. For inline grammars the type parameter specifies a media type that governs the interpretation of the content of the <grammar> element.
The following is an example of inline grammar defined by the XML Form of the W3C Speech Recognition Grammar Specification [SRGS].
<grammar mode="voice" xml:lang="en-US" version="1.0" root="command">
<!-- Command is an action on an object -->
<!-- e.g. "open a window" -->
<rule id="command" scope="public">
<ruleref uri="#action"/> <ruleref uri="#object"/>
</rule>
<rule id="action">
<one-of>
<item> open </item>
<item> close </item>
<item> delete </item>
<item> move </item>
</one-of>
</rule>
<rule id="object">
<item repeat="0-1">
<one-of> <item> the </item> <item> a </item> </one-of>
</item>
<one-of>
<item> window </item>
<item> file </item>
<item> menu </item>
</one-of>
</rule>
</grammar>
The following is the equivalent example of the inline grammar defined by the ABNF Form of the W3C Speech Recognition Grammar Specification [SRGS]. Because VoiceXML platforms are not required to support this format it may be less portable.
<grammar mode="voice" type="application/srgs"> #ABNF 1.0; language en-US; mode voice; root $command; public $command = $action $object; $action = open | close | delete | move; $object = [the | a] (window | file | menu); </grammar>
An external grammar is specified by an element of the form
<grammar src="URI" type="media-type"/>
The media type is optional in this case because the interpreter context will attempt to determine the type dynamically if it is unspecified (for instance, using server-specified media type, file extension, or content introspection).
If the src attribute is defined and there is an inline grammar as content of a grammar element then an error.badfetch event is thrown.
The following is an example of a reference to an external grammar written in the XML Form of the W3C Speech Recognition Grammar Specification [SRGS].
<grammar type="application/srgs+xml" src="http://www.grammar.example.com/date.grxml"/>
The following example is the equivalent grammar reference for a grammar that is authored using the ABNF Form of the W3C Speech Recognition Grammar Specification [SRGS].
<grammar type="application/srgs" src="http://www.grammar.example.com/date.gram"/>
A weight for the grammar can be specified by the weight attribute:
<grammar weight="0.6" src="form.grxml" type="application/srgs+xml"/>
Grammar elements, including those in link, field and form elements, can have a weight attribute. The grammar can be inline, external or built-in.
Weights follow the definition of weights on alternatives in the W3C Speech Recognition Grammar Specification [SRGS §2.4.1]. A weight is a simple positive floating point values without exponentials. Legal formats are "n", "n.", ".n" and "n.n" where "n" is a sequence of one or many digits.
A weight is nominally a multiplying factor in the likelihood domain of a speech recognition search. A weight of "1.0" is equivalent to providing no weight at all. A weight greater than "1.0" positively biases the grammar and a weight less than "1.0" negatively biases the grammar. If unspecified, the default weight for any grammar is "1.0". If no weight is specified for any grammar element then all grammars are equally likely.
<link event="help">
<grammar weight="0.5" mode="voice" version="1.0" root="help">
<rule id="help" scope="public">
<item repeat="0-1">Please</item> help
</rule>
</grammar>
</link>
<form>
<grammar src="form.grxml" type="application/srgs+xml"/>
<field name="expireDate">
<grammar weight="1.2" src="http://www.example.org/grammar/date"/>
</field>
</form>
In the example above, the semantics of weights is equivalent to the following XML grammar.
<grammar root="r1" type="application/srgs+xml">
<rule id="r1">
<one-of>
<item weight="0.5"> <ruleref uri="#help"/> </item>
<item weight="1.0"> <ruleref uri="form.grxml"/> </item>
<item weight="1.2"> <ruleref uri="http://www.example.org/grammar/date"/></item>
</one-of>
</rule>
<rule id="help">
<item repeat="0-1">Please</item> help
</rule>
</grammar>
Implicit grammars, such as those in options, do not support weights - use the <grammar> element instead for control over grammar weight.
Grammar weights only affect grammar processing. They do not directly affect the post processing of grammar results, including grammar precedence when user input matches multiple active grammar (see Section 3.1.4).
A weight has no effect on DTMF grammars (See Section 3.1.2). Any weight attribute specified in a grammar element whose mode attribute is dtmf is ignored.
<!-- weight will be ignored --> <grammar mode="dtmf" weight="0.3" src="http://www.example.org/dtmf/number"/>
Appropriate weights are difficult to determine, and guessing weights does not always improve recognition performance. Effective weights are usually obtained by study of real speech and textual data on a paricular platform. Furthermore, a grammar weight is platform specific. Note that different ASR engines may treat the same weight value differently. Therefore, the weight value that works well on particular platform may generate different results on other platforms.
Attributes of <grammar> inherited from the W3C Speech Recognition Grammar Specification [SRGS] are:
| version | Defines the version of the grammar. |
|---|---|
| xml:lang | The language identifier of the grammar (for example, "fr-CA" for Canadian French.) If omitted, the value is inherited down from the document hierarchy. |
| mode | Defines the mode of the grammar following the modes of the W3C Speech Recognition Grammar Specification [SRGS]. |
| root | Defines the rule which acts as the root rule of the grammar. |
| tag-format | Defines the tag content format for all tags within the grammar. |
| xml:base | Declares the base URI from which relative URIs in the grammar are
resolved.
This base declaration has precedence over the <vxml> base URI declaration. If a local declaration is omitted, the value is inherited down the document hierarchy. |
The use and interpretation of these attributes is determined as follows:
Attributes of <grammar> added by VoiceXML 2.0 are:
| src | The URI specifying the location of the grammar and optionally a rulename within that grammar, if it is external. The URI is interpreted as a rule reference as defined in Section 2.2 of the Speech Recognition Grammar Specification [SRGS] but not all forms of rule reference are permitted from within VoiceXML. The rule reference capabilities are described in detail below this table. |
|---|---|
| scope | Either "document", which makes the grammar active in all dialogs of the current document (and relevant application leaf documents), or "dialog", to make the grammar active throughout the current form. If omitted, the grammar scoping is resolved by looking at the parent element. See Section 3.1.3 for details on scoping including precedence behavior. |
| type |
The media type of the grammar. This value takes precedence over other possible sources of the media type (for instance, the "Content-type" field in an HTTP or RTSP exchange, or the file extension). If this is omitted, the interpreter context will attempt to determine the type dynamically (for instance, using server-specified media type, file extension, or content introspection). If the content of the grammar is contained within the element and no media type is specified, the media type is assumed to be an XML grammar. If the grammar source does not contain valid content of the selected media type, an error is thrown when the grammar is used. The tentative media types for the W3C grammar format are "application/srgs+xml" for the XML form and "application/srgs" for ABNF grammars. |
| weight | Specifies the weight of the grammar. See Section 3.1.1.3 |
| fetchhint | See Section 6.1. This defaults to the grammarfetchhint property. |
| fetchtimeout | See Section 6.1. This defaults to the fetchtimeout property. |
| maxage | See Section 6.1. This defaults to the grammarmaxage property. |
| maxstale | See Section 6.1. This defaults to the grammarmaxstale property. |
Either an "src" attribute or a inline grammar (but not both) must be specified; otherwise, an error.badfetch event is thrown.
The <grammar> element is also extended in VoiceXML 2.0 to allow PCDATA for inline grammar formats besides the XML Form of the W3C Speech Recognition Grammar Specification [SRGS].
When referencing an external grammar, the value of the src attribute is a URI specifying the location of the grammar with an optional fragment for the rulename. Section 2.2 of the Speech Recognition Grammar Specification [SRGS] defines several forms of rule reference. The following are the forms that are permitted on a grammar element in VoiceXML.
The following are the forms of rule reference defined by [SRGS] that are not supported in VoiceXML 2.0.
The <grammar> element can be used to provide a DTMF grammar that
specifies a set of key presses that a user may use to perform an action or supply information, and
VoiceXML platforms are required to support the DTMF grammar XML format defined in Appendix D of the [SRGS] to advance application portability.
A DTMF grammar is distinguished from a speech grammar by the mode attribute on the <grammar> element. An "xml:lang" attribute has no effect on DTMF grammar handling. In other respects speech and DTMF grammars are handled identically including the ability to define the grammar inline, or by an external grammar reference. The media type handling, scoping and fetching are also identical.
The following is an example of a simple inline XML DTMF grammar that accepts as input either "1 2 3" or "#".
<grammar mode="dtmf" version="1.0" root="root">
<rule id="root" scope="public">
<one-of>
<item> 1 2 3 </item>
<item> # </item>
</one-of>
</rule>
</grammar>
Input item grammars are always scoped to the containing input item; that is, they are active only when the containing input item was chosen during the select phase of the FIA. Grammars contained in input items cannot specify a scope; if they do, an error.badfetch is thrown.
Link grammars are given the scope of the element that contains the link. Thus, if they are defined in the application root document, links are also active in any other loaded application document. Grammars contained in links cannot specify a scope; if they do, an error.badfetch is thrown.
Form grammars are by default given dialog scope, so that they are active only when the user is in the form. If they are given scope document, they are active whenever the user is in the document. If they are given scope document and the document is the application root document, then they are also active whenever the user is in another loaded document in the same application. A grammar in a form may be given document scope either by specifying the scope attribute on the form element or by specifying the scope attribute on the <grammar> element. If both are specified, the grammar assumes the scope specified by the <grammar> element.
Menu grammars are also by default given dialog scope, and are active only when the user is in the menu. But they can be given document scope and be active throughout the document, and if their document is the application root document, also be active in any other loaded document belonging to the application. Grammars contained in menu choices cannot specify a scope; if they do, an error.badfetch is thrown.
Sometimes a form may need to have some grammars active throughout the document, and other grammars that should be active only when in the form. One reason for doing this is to minimize grammar overlap problems. To do this, each individual <grammar> element can be given its own scope if that scope should be different than the scope of the <form> element itself:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form scope="document">
<grammar type="application/srgs">
#ABNF 1.0;
language en-gb;
mode voice;
root $command;
public $command = one | two | three;
</grammar>
<grammar type="application/srgs" scope="dialog">
#ABNF 1.0;
language en-gb;
mode voice;
root $command2;
public $command2 = four | five | six;
</grammar>
</form>
</vxml>
When the interpreter waits for input as a result of visiting an input item, the following grammars are active:
grammars for that input item, including grammars contained in links in that input item;
grammars for its form, including grammars contained in links in that form;
grammars contained in links in its document, and grammars for menus and other forms in its document which are given document scope;
grammars contained in links in its application root document, and grammars for menus and forms in its application root document which are given document scope.
grammars defined by platform default event handlers, such as help, exit and cancel.
In the case that an input matches more than one active grammar, the list above defines the precedence order. If the input matches more than one active grammar with the same precedence, the precedence is determined using document order. If no grammars are active when an input is expected, the platform must throw an error.semantic event. The error will be thrown in the context of the executing element. Menus behave with regard to grammar activation like their equivalent forms (see Section 2.2.1).
If the form item is modal (i.e., its modal attribute is set to true), all grammars except its own are turned off while waiting for input. If the input matches a grammar in a form or menu other than the current form or menu, control passes to the other form or menu. If the match causes control to leave the current form, all current form data is lost.
Grammar activation is not affected by the inputmodes property. For instance, if the inputmodes property restricts input to just voice, DTMF grammars will still be activated, but cannot be matched.
The Speech Recognition Grammar Specification defines a tag element which contains content for semantic interpretation of speech and DTMF grammars (see Section 2.6 of [SRGS]).
The Semantic Interpretation for Speech Recognition specification [SISR] describes a syntax and semantics for tags and specifies how a semantic interpretation for user input can be computed using the content of tags associated with the matched tokens and rules. The semantic interpretation may be mapped into VoiceXML as described in Section 3.1.6.
The semantic interpretation returned from a Speech Recognition Grammar Specification [SRGS] grammar must be mapped into one or more VoiceXML ECMAScript variables. The process by which this occurs differs slightly for form- and field-level results; these differences will be explored in the next sections. The format of the semantic interpretation, using either the proposed Natural Language Semantics Markup Language [NLSML] or the ECMAScript-like output format of [SISR], has no impact on this discussion. For the purposes of this discussion, the actual result returned from the recognizer is assumed to have been mapped into an ECMAScript-like format which is identical to the representation in application.lastresult$.interpretation as discussed in Section 5.1.5.
It is possible that a grammar will match but not return a semantic interpretation. In this case, the platform will use the raw text string for the utterance as the semantic result. Otherwise, this case is handled exactly as if the semantic interpretation consisted of a simple value.
Every input item has an associated slot name which may be used to extract part of the full semantic interpretation. The slot name is the value of the 'slot' attribute, if present (only possible for <field> elements), or else the value of the 'name' attribute. If neither slot nor name is present, then the slot name is undefined.
The slot name is used during the Process Phase of the FIA to determine whether or not an input item matches. A match occurs when either the slot name is the same as a top-level property or a slot name is used to select a sub-property. A property having an undefined value (i.e. ECMAScript undefined) will not match. Likewise, slot names which are undefined will never match. Examples are given in Section 3.1.6.3.
The next sections concern mapping form-level and field-level results. There is also a brief discussion of other issues such as the NL Semantics to ECMAScript mapping, transitioning information from ASR results to VoiceXML, and dealing with mismatches between the interpretation result and the VoiceXML form.
Grammars specified at the form-level produce a form-level result which may fill multiple input items simultaneously. This may occur anytime, whether in an <initial> element or in an input item, that the user's input matches an active form-level grammar.
Consider the interpretation result from the sentence "I would like a coca cola and three large pizzas with pepperoni and mushrooms." The semantic interpretation may be copied into application.lastresult$.interpretation as
{
drink: "coke"
pizza: {
number: "3"
size: "large"
topping: [
"pepperoni"
"mushrooms"
]
}
}
The following table illustrates how this result from a form-level grammar would be assigned to various fields within the form. Note that all input items that can be filled in from the interpretation are filled in simultaneously . The existing values of matching input item variables will be overwritten, and these items will be marked for <filled> processing during the FIA's Process Phase as described in Section 2.4 and Appendix C.
| VoiceXML field | Assigned ECMAScript value | Explanation |
|---|---|---|
| 1. <field name="drink"/> | "coke" | By default a field is assigned the top-level result property whose name matches the field name. |
| 2. <field name="..." slot="drink"/> | "coke" | If specified, the slot overrides the field name for selecting the result property. |
| 3. <field name="pizza"/> --or-- <field name="..." slot="pizza"/> |
{number: "3", size: "large", topping: ["pepperoni", "mushroom"]} | The field name or slot may select a property that is a non-scalar ECMAScript variable in the same way that a scalar value is selected in the previous example. However the application must then handle inspecting the components of the object. This does not take advantage of the VoiceXML form-filling algorithm, in that missing slots in the result would not be automatically prompted for. This may be sufficient in situations where the server is prepared to deal with a structured object. Otherwise, an application may prefer to use the method described in the next example. |
| 4. <field name="..." slot="pizza.number"/> <field name="..." slot="pizza.size"/> |
"3" "large" |
The slot may be used to select a sub-property of the result. This approach distributes the result among a number of fields. |
| 5. <field name="..." slot="pizza.topping"/> | ["pepperoni", "mushroom"] | The selected property may be a compound object. |
These examples can be explained by rules that are compatible with and are straightforward extensions of the VoiceXML 1.0 "name" and "slot" attributes:
Grammars specified within an input item produce a field-level result which may fill only the particular input item in which they are contained. These grammars are active only when the FIA is visiting that specific input item. This is useful, for instance, in directed dialogs where a user is prompted individually for each input item.
A field-level result fills the associated input item in the following manner:
This process allows an input item to extract a particular property from the semantic interpretation. This may be combined with <filled> for achieve even greater control.
<field name="getdate">
<prompt>On what date would you like to fly?</prompt>
<grammar src="http://server.example.com/date.grxml"/>
<!-- this grammar always returns an object containing
string values for the properties day, month, and year -->
<filled>
<assign name="getdate.datestring"
expr="getdate.year + getdate.month + getdate.day"/>
</filled>
</field>
A matching slot name allows an input item to extract part of a semantic interpretation. Consider this modified result from the earlier pizza example.
application.lastresult$.interpretation =
{ drink: { size: 'large', liquid: 'coke' }
pizza: { number: '3', size: 'large',
topping: ['pepperoni', 'mushroom' ] }
sidedish: undefined
}
The table below revisits the definition of when the slot name matches a property in the result.
| slot name | match or not? |
| undefined | does not match |
| drink | matches; top level property |
| pizza | matches; top level property |
| sidedish | does not match; no defined value |
| size | does not match; not a top-level property |
| pizza.size | matches; sub-property |
| pizza.liquid | does not match |
It is also possible to compare the behaviors of form-level and field-level results. For this purpose, consider the following document:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="exampleForm">
<grammar src="formlevel.grxml"/>
<initial> Say something. </initial>
<field name="x">
<grammar src="fieldx.grxml"/>
</field>
<field name="z" slot="y">
<grammar src="fieldz.grxml"/>
</field>
</form>
</vxml>
This defines two input item variables, 'x' and 'z'. The corresponding slot names are 'x' and 'y' respectively. The next table describes the assignment of these variables depending on which grammar is recognized and what semantic result is returned. The shorthand valueX is used to indicate 'the structured object or simple result value associated with the property x'.
|
application. lastresult$. interpretation
|
form-level result (formlevel.grxml) |
field-level result in field x (fieldx.grxml) |
field-level result in field z (fieldz.grxml) |
| = 'hello' |
no assignment; cycle FIA |
x = 'hello' | z = 'hello' |
| = { x: valueX } | x = valueX | x = valueX | z = { x: valueX } |
| = { y: valueY } | z = valueY | x = { y: valueY } | z = valueY |
| = { z: valueZ } |
no assignment; cycle FIA |
x = { z: valueZ } | z = { z: valueZ } |
| = { x: valueX, y: valueY, z: valueZ } |
x = valueX z = valueY |
x = valueX | z = valueY |
| = { a: valueA b: valueB } |
no assignment; cycle FIA |
x = { a: valueA, b: valueB } |
z = { a: valueA, b: valueB } |
At the form level, simple results like the string 'hello' cannot match any input items; structured objects assign all input item variables with matching slot names. At the field level, simple results are always assigned to the input item variable; structured objects will extract the matching property, if it exists, or will otherwise be assigned the entire semantic result.
1. Mapping from NL semantics to ECMAScript: If the NL Semantics Markup Language ([NLSML]) is used, a mapping needs to be defined from the NLSML representation to ECMAScript objects. Since both types of representation have similar nested structures, this mapping is fairly straightforward. This mapping is discussed in detail in the NL Semantics specification.
2. Transitioning semantic results from ASR to VoiceXML: The result of processing the semantic tags of a W3C ASR grammar is the value of the attribute of the root rule when all semantic attachment evaluations have been completed. In addition, the root rule (like all non-terminals) has an associated "text" variable which contains the series of tokens in the utterance that is governed by that non-terminal. In the process of making ASR results available to VoiceXML documents, the VoiceXML platform is not only responsible for filling in the VoiceXML fields based on the value of the attribute of the root rule, as described above, but also for filling in the shadow variables of the field. The name$.utterance shadow variable of the field should be the same as the "text" variable value for the ASR root rule. The platform is also responsible for instantiating the value of the shadow variable "name$.confidence" based on information supplied by the ASR platform, as well as the value of "name$.inputmode" based on whether DTMF or speech was processed. Finally, the platform is responsible for making this same information available in the "application.lastresult$" variable, defined in Section 5.1.5 (specifically, "application.lastresult$.utterance", "application.lastresult$.inputmode", and "application.lastresult$.interpretation"), with the exception of application.lastresult$.confidence, which the platform sets to the confidence of the entire utterance interpretation.
3. Mismatches between semantic results and VoiceXML fields: Mapping semantic results to VoiceXML depends on a tight coordination between the ASR grammar and the VoiceXML markup. Since in the current framework there's nothing that enforces consistency between a grammar and the associated VoiceXML dialog, mismatches can occur due to developer oversight. Since the dialog's behaviour during these mismatches is difficult to distinguish from certain normal situations, verifying consistency of information is extremely important. Some examples of mismatches:
In order to address these potential problems, the committee is looking at various approaches to ensuring consistency between the grammar and the VoiceXML.
The <prompt> element controls the output of synthesized speech and prerecorded audio. Conceptually, prompts are instantaneously queued for play, so interpretation proceeds until the user needs to provide an input. At this point, the prompts are played, and the system waits for user input. Once the input is received from the speech recognition subsystem (or the DTMF recognizer), interpretation proceeds.
The <prompt> element has the following attributes:
| bargein | Control whether a user can interrupt a prompt. This defaults to the value of the bargein property. See Section 6.3.4. |
|---|---|
| bargeintype | Sets the type of bargein to be 'speech', or 'hotword'. This defaults to the value of the bargeintype property. See Section 6.3.4. |
| cond | An expression that must evaluate to true after conversion to boolean in order for the prompt to be played. Default is true. |
| count | A number that allows you to emit different prompts if the user is doing something repeatedly. If omitted, it defaults to "1". |
| timeout | The timeout that will be used for the following user input. The value is a Time Designation (see Section 6.5). The default noinput timeout is platform specific. |
| xml:lang | The language identifier for the prompt. If omitted, it defaults to the value specified in the document's "xml:lang" attribute. |
| xml:base | Declares the base URI from which relative URIs in the prompt are resolved. This base declaration has precedence over the <vxml> base URI declaration. If a local declaration is omitted, the value is inherited down the document hierarchy. |
The content of the <prompt> element is modelled on the W3C Speech Synthesis Markup Language 1.0 [SSML].
The following speech markup elements are defined in [SSML] and are available in VoiceXML 2.0. Refer to the W3C Speech Synthesis Markup Language 1.0 [SSML] for definitions and examples.
| Element | Purpose | Section (in SSML spec) |
|---|---|---|
| <audio> | Specifies audio files to be played and text to be spoken. | 2.3.1 |
| <break> | Specifies a pause in the speech output. | 2.2.3 |
| <desc> | Provides a description of a non-speech audio source in <audio>. | 2.3.3 |
| <emphasis> | Specifies that the enclosed text should be spoken with emphasis. | 2.2.2 |
| <lexicon> | Specifies a pronunciation lexicon for the prompt. | 3.3 |
| <mark> | Ignored by VoiceXML platforms. | 2.3.2 |
| <metadata> | Specifies XML metadata content for the prompt. | 3.4 |
|
<paragraph> |
Identifies the enclosed text as a paragraph, containing zero or more sentences | 2.1.3 |
| <phoneme> | Specifies a phonetic pronunciation for the contained text. | 2.1.5 |
| <prosody> | Specifies prosodic information for the enclosed text. | 2.2.4 |
| <say-as> | Specifies the type of text construct contained within the element. | 2.1.4 |
| <sentence> (alias <s>) |
Identifies the enclosed text as a sentence. | 2.1.3 |
| <sub> | Specifies replacement spoken text for the contained text. | 2.1.6 |
| <voice> | Specifies voice characteristics for the spoken text. | 2.2.1 |
When used in VoiceXML, additional properties are defined for the <audio> (Section 4.1.3) and <say-as> (Appendix P) elements. VoiceXML also allows <enumerate> and <value> elements to appear within the <prompt> element.
The VoiceXML platform must be a Conforming Speech Synthesis Markup Language Processor as defined in the [SSML]. While this requires a platform to process documents with one or more "xml:lang" attributes defined, it does not require that the platform must be multi-lingual. When an unsupported language is encountered, the platform throws an error.unsupported.language event which specifies the language in its message variable.
You’ve seen prompts in the previous examples:
<prompt>Please say your city.</prompt>
You can leave out the <prompt> ... </prompt> if:
There is no need to specify a prompt attribute (like bargein), and
The prompt consists entirely of PCDATA (contains no speech markups) or consists of just an <audio> or <value> element.
For instance, these are also prompts:
Please say your city. <audio src="say_your_city.wav"/>
But in this example, the enclosing prompt elements are required due to the embedded speech markups:
<prompt>Please <emphasis>say</emphasis> your city.</prompt>
Prompts can consist of any combination of prerecorded files, audio streams, or synthesized speech:
<prompt>
Welcome to the Bird Seed Emporium.
<audio src="rtsp://www.birdsounds.example.com/thrush.wav"/>
We have 250 kilogram drums of thistle seed for
<say-as interpret-as="currency">$299.95</say-as>
plus shipping and handling this month.
<audio src="http://www.birdsounds.example.com/mourningdove.wav"/>
</prompt>
Audio can be played in any prompt. The audio content can be specified via a URI, and in VoiceXML it can also be in an audio variable previously recorded:
<prompt> Your recorded greeting is <audio expr="greeting"/> To rerecord, press 1. To keep it, press pound. To return to the main menu press star M. To exit press star, star X. </prompt>
The <audio> element can have alternate content in case the audio sample is not available:
<prompt>
<audio src="welcome.wav">
<emphasis>Welcome</emphasis> to the Voice Portal.
</audio>
</prompt>
If the audio file cannot be played (e.g. 'src' referencing or 'expr' evaluating to an invalid URI, a file with an unsupported format, etc), the content of the audio element is played instead. The content may include text, speech markup, or another audio element. If the audio file cannot be played and the content of the audio element is empty, no audio is played and no error event is thrown.
If <audio> contains an 'expr' attribute evaluating to ECMAScript undefined, then the element, including its alternate content, is ignored. This allows a developer to specify <audio> elements with dynamically assigned content which, if the element is not required, can be ignored by assigning its 'expr' a null value. For example, the following code shows how this could be used to play back a hand of cards using concatenated audio clips:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form>
<!-- script contains the function sayCard(type,position)
which takes as input the type of card description (audio or text) and
its position in an array, and returns the selected card description in
the specified array position; if there is no description in the
requested array position, then returns EMCAScript undefined
-->
<script src="cardgame.js"/>
<field name="takecard">
<grammar type="application/srgs+xml" src="/grammars/boolean.grxml"/>
<prompt>
<audio src="you_have.wav">You have the following cards: </audio>
<!-- maximum of hand of 5 cards is described -->
<audio expr="sayCard(audio,1)"><value expr="sayCard(text,1)"/></audio>
<audio expr="sayCard(audio,2)"><value expr="sayCard(text,2)"/></audio>
<audio expr="sayCard(audio,3)"><value expr="sayCard(text,3)"/></audio>
<audio expr="sayCard(audio,4)"><value expr="sayCard(text,4)"/></audio>
<audio expr="sayCard(audio,5)"><value expr="sayCard(text,5)"/></audio>
<audio src="another.wav">Would you like another card?</audio>
</prompt>
<filled>
<if cond="takecard">
<script>takeAnotherCard()</script>
<clear/>
<else/>
<goto next="./make_bid.html"/>
</if>
</filled>
</field>
</form>
</vxml>
Attributes of <audio> defined in [SSML] are:
| src | The URI of the audio prompt. See Appendix E for required audio file formats; additional formats may be used if supported by the platform. |
|---|
Attributes of <audio> defined only in VoiceXML are:
| fetchtimeout | See Section 6.1. This defaults to the fetchtimeout property. |
|---|---|
| fetchhint | See Section 6.1. This defaults to the audiofetchhint property. |
| maxage | See Section 6.1. This defaults to the audiomaxage property. |
| maxstale | See Section 6.1. This defaults to the audiomaxstale property. |
| expr | An ECMAScript expression which determines the source of the audio to be played. The expression may be either a reference to audio previously recorded with the <record/> field item or evaluate to the URI of an audio resource to fetch. |
Exactly one of "src" or "expr" must be specified; otherwise, an error.badfetch event is thrown.
Note that it is a platform optimization to stream audio: i.e. the platform may begin processing audio content as it arrives and not to wait for full retrieval. The "prefetch" fetchhint can be used to request full audio retrieval prior to playback.
The <value> element is used to insert the value of an expression into a prompt. It has one attribute:
| expr | The expression to render. |
|---|
For example if n is 12, the prompt
<prompt> <value expr="n*n"/> is the square of <value expr="n"/>. </prompt>
will result in the text string "144 is the square of 12" being passed to the speech synthesis engine.
The manner in which the value attribute is played is controlled by the surrounding speech synthesis markup. For instance, a value can be played as a date in the following example:
<var name="date" expr="'2000/1/20'"/>
<prompt>
<say-as interpret-as="date"> <value expr="date"/> </say-as>
</prompt>
The text inserted by the <value> element is not subject to any special interpretation; in particular, it is not parsed as an [SSML] document or document fragment. XML special characters (&, >, and <) are not treated specially and do not need to be escaped. The equivalent effect may be obtained by literally inserting the text computed by the <value> element in a CDATA section. For example, when the following variable assignment:
<script>
<![CDATA[
e1 = 'AT&T';
]]>
</script>
is referenced in a prompt element as
<prompt> The price of <value expr="e1"/> is $1. </prompt>
the following output is produced.
The price of AT&T is $1.
If an implementation platform supports bargein, the application author can specify whether a user can interrupt, or "bargein" on, a prompt using speech or DTMF input. This speeds up conversations, but is not always desired. If the application author requires that the user must hear all of a warning, legal notice, or advertisement, bargein should be disabled. This is done with the bargein attribute:
<prompt bargein="false"><audio src="legalese.wav"/></prompt>
Users can interrupt a prompt whose bargein attribute is true, but must wait for completion of a prompt whose bargein attribute is false. In the case where several prompts are queued, the bargein attribute of each prompt is honored during the period of time in which that prompt is playing. If bargein occurs during any prompt in a sequence, all subsequent prompts are not played (even those whose bargein attribute is set to false). If the bargein attribute is not specified, then the value of the bargein property is used if set.
When the bargein attribute is false, input is not buffered while the prompt is playing, and any DTMF input buffered in a transition state is deleted from the buffer (Section 4.1.8 describes input collection during transition states).
Note that not all speech recognition engines or implementation platforms support bargein. For a platform to support bargein, it must support at least one of the bargein types described in Section 4.1.5.1.
When bargein is enabled, the bargeintype attribute can be used to suggest the type of bargein the platform will perform in response to voice or DTMF input. Possible values for this attribute are:
| speech | The prompt will be stopped as soon as speech or DTMF input is detected. The prompt is stopped irrespective of whether or not the input matches a grammar. |
|---|---|
| hotword | The prompt will not be stopped until a complete match of an active grammar is detected. Input that does not match a grammar is ignored; as a consequence, a nomatch event will never be generated in the case of hotword bargein. |
If the bargeintype attribute is not specified, then the value of the bargeintype property is used. Implementations that claim to support bargein are required to support at least one of these two types. Mixing these types within a single queue of prompts can result in unpredictable behavior and is discouraged.
In the case of "speech" bargeintype, the exact meaning of "speech input" is necessarily implementation-dependent, due to the complexity of speech recognition technology. It is expected that the prompt will be stopped as soon as the platform is able to reliably determine that the input is speech. Stopping the prompt as early as possible is desireable because it avoids the "stutter" effect in which a user stops in mid-utterance and re-starts if he does not believe that the system has heard him.
Tapered prompts are those that may change with each attempt. Information-requesting prompts may become more terse under the assumption that the user is becoming more familiar with the task. Help messages become more detailed perhaps, under the assumption that the user needs more help. Or, prompts can change just to make the interaction more interesting.
Each input item, <initial>, and menu has an internal prompt counter that is reset to one each time the form or menu is entered. Whenever the system uses a prompt, its associated prompt counter is incremented. This is the mechanism supporting tapered prompts.
For instance, here is a form with a form level prompt and field level prompts:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="tapered">
<block>
<prompt bargein="false">
Welcome to the ice cream survey.
</prompt>
</block>
<field name="flavor">
<grammar mode="voice" version="1.0" root="root">
<rule id="root" scope="public">
<one-of>
<item>vanilla </item>
<item>chocolate</item>
<item>strawberry</item>
</one-of>
</rule>
</grammar>
<prompt count="1">What is your favorite flavor?</prompt>
<prompt count="3">Say chocolate, vanilla, or strawberry.</prompt>
<help>Sorry, no help is available.</help>
</field>
</form>
</vxml>
A conversation using this form follows:
C: Welcome to the ice cream survey.
C: What is your favorite flavor? (the "flavor" field’s prompt counter is 1)
H: Pecan praline.
C: I do not understand.
C: What is your favorite flavor? (the prompt counter is now 2)
H: Pecan praline.
C: I do not understand.
C: Say chocolate, vanilla, or strawberry. (prompt counter is 3)
H: What if I hate those?
C: I do not understand.
C: Say chocolate, vanilla, or strawberry. (prompt counter is 4)
H: ...
When it is time to select a prompt, the prompt counter is examined. The child prompt with the highest count attribute less than or equal to the prompt counter is used. If a prompt has no count attribute, a count of "1" is assumed.
A conditional prompt is one that is spoken only if its condition is satisfied. In this example, a prompt is varied on each visit to the enclosing form.
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="another_joke">
<var name="r" expr="Math.random()"/>
<field name="another">
<grammar type="application/srgs+xml" src="/grammars/boolean.grxml"/>
<prompt cond="r < .50">
Would you like to hear another elephant joke?
</prompt>
<prompt cond="r >= .50">
For another joke say yes. To exit say no.
</prompt>
<filled>
<if cond="another">
<goto next="#pick_joke"/>
</if>
</filled>
</field>
</form>
</vxml>
When a prompt must be chosen, a set of prompts to be queued is chosen according to the following algorithm:
All elements that remain on the list will be queued for play.
The timeout attribute specifies the interval of silence allowed while waiting for user input after the end of the last prompt. If this interval is exceeded, the platform will throw a noinput event. This attribute defaults to the value specified by the timeout property (see Section 6.3.4) at the time the prompt is queued. In other words, each prompt has its own timeout value.
The reason for allowing timeouts to be specified as prompt attributes is to support tapered timeouts. For example, the user may be given five seconds for the first input attempt, and ten seconds on the next.
The prompt timeout attribute determines the noinput timeout for the following input:
<prompt count="1"> Pick a color for your new Model T. </prompt> <prompt count="2" timeout="120s"> Please choose color of your new nineteen twenty four Ford Model T. Possible colors are black, black, or black. Please take your time. </prompt>
If several prompts are queued before a field input, the timeout of the last prompt is used.
A VoiceXML interpreter is at all times in one of two states:
The waiting and transitioning states are related to the phases of the Form Interpretation Algorithm as follows:
This distinction of states is made in order to greatly simplify the programming model. In particular, an important consequence of this model is that the VoiceXML application designer can rely on all executable content (such as the content of <filled> and <block> elements) being run to completion, because it is executed while in the transitioning state, which may not be interrupted by input.
While in the transitioning state various prompts are queued, either by the <prompt> element in executable content or by the <prompt> element in form items. In addition, audio may be queued by the fetchaudio attribute. The queued prompts and audio are played either
Note that when a prompt's bargein attribute is false, input is not collected and DTMF input buffered in a transition state is deleted (see Section 4.1.5).
Before the interpreter exits all queued prompts are played to completion. The interpreter remains in the transitioning state and no input is accepted while the interpreter is exiting.
It is a permissible optimization to begin playing prompts queued during the transitioning state before reaching the waiting state, provided that correct semantics are maintained regarding processing of the input audio received while the prompts are playing, for example with respect to bargein and grammar processing.
The following examples illustrate the operation of these rules in some common cases.
Typical non-fetching case: field, followed by executable content (such as <block> and <filled>), followed by another field.
in document d0
<field name="f0"/>
<block>
executable content e1
queues prompts {p1}
</block>
<field name="f2">
queues prompts {p2}
enables grammars {g2}
</field>
As a result of input received while waiting in field f0 the following actions take place:
Typical fetching case: field, followed by executable content (such as <block> and <filled>) ending with a <goto> that specifies fetchaudio, ending up in a field in a different document that is fetched from a server.
in document d0
<field name="f0"/>
<block>
executable content e1
queues prompts {p1}
ends with goto f2 in d1 with fetchaudio fa
</block>
in document d1
<field name="f2">
queues prompts {p2}
enables grammars {g2}
</field>
As a result of input received while waiting in field f0 the following actions take place:
As in Case 2, but no fetchaudio is specified.
in document d0
<field name="f0"/>
<block>
executable content e1
queues prompts {p1}
ends with goto f2 in d1 (no fetchaudio specified)
</block>
in document d1
<field name="f2">
queues prompts {p2}
enables grammars {g2}
</field>
As a result of input received while waiting in field f0 the following actions take place:
VoiceXML variables are in all respects equivalent to ECMAScript variables: they are part of the same variable space. VoiceXML variables can be used in a <script> just as variables defined in a <script> can be used in VoiceXML. Declaring a variable using <var> is equivalent to using a 'var' statement in a <script> element. <script> can also appear everywhere that <var> can appear. VoiceXML variables are also declared by form items.
The variable naming convention is as in ECMAScript, but names beginning with the underscore character ("_") and names ending with a dollar sign ("$") are reserved for internal use. VoiceXML variables, including form item variables, must not contain ECMAScript reserved words. They must also follow ECMAScript rules for referential correctness. For example, variable names must be unique and their declaration must not include a dot - "var x.y" is an illegal declaration in ECMAScript. Variable names which violate naming conventions or ECMAScript rules cause an 'error.semantic' event to be thrown.
Variables are declared by <var> elements:
<var name="home_phone"/> <var name="pi" expr="3.14159"/> <var name="city" expr="'Sacramento'"/>
They are also declared by form items:
<field name="num_tickets"> <grammar type="application/srgs+xml" src="/grammars/number.grxml"/> <prompt>How many tickets do you wish to purchase?</prompt> </field>
Variables declared without an explicit initial value are initialized to the ECMAScript undefined value. Variables must be declared before being used either in VoiceXML or ECMAScript. Use of an undeclared variable results in an ECMAScript error which is thrown as an error.semantic. Variables declared using "var" in ECMAScript can be used in VoiceXML, just as declared VoiceXML variables can be used in ECMAScript.
In a form, the variables declared by <var> and those declared by form items are initialized when the form is entered. The initializations are guaranteed to take place in document order, so that this, for example, is legal:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="test">
<var name="one" expr="1"/>
<field name="two" expr="one+1">
<grammar type="application/srgs+xml" src="/grammars/number.grxml"/>
</field>
<var name="three" expr="two+1"/>
<field name="go_on" type="boolean">
<prompt>Say yes or no to continue</prompt>
</field>
</form>
</vxml>
When the user visits this <form>, the form’s initialization first declares the variable one and sets its value to 1. Then it declares the field item variable two and gives it the value 2. Then the initialization logic declares the variable three and gives it the value 3. The form interpretation algorithm then enters its main interpretation loop and begins at the go_on field.
VoiceXML uses an ECMAScript scope chain to allow variables to be declared at different levels of hierarchy in an application. For instance, a variable declared at document scope can be referenced anywhere within that document, whereas a local variable declared in a catch element is only available within that catch element. In order to preserve these scoping semantics, all ECMAScript variables must be declared. Use of an undeclared variable results in an ECMAScript error which is thrown as an error.semantic.
Variables can be declared in following scopes:
| session | These are read-only variables that pertain to an entire user session. They are declared and set by the interpreter context. New session variables cannot be declared by VoiceXML documents. See Section 5.1.4. |
|---|---|
| application | These are declared with <var> and <script> elements that are children of the application root document's <vxml> element. They are initialized when the application root document is loaded. They exist while the application root document is loaded, and are visible to the root document and any other loaded application leaf document. Note that while executing inside the application root document document.x is equivalent to application.x. |
| document | These variables are declared with <var> and <script> elements that are children of the document’s <vxml> element. They are initialized when the document is loaded. They exist while the document is loaded. They are visible only within that document, unless the document is an application root, in which case the variables are visible by leaf documents through the application scope only. |
| dialog | Each dialog (<form> or <menu>) has a dialog scope that exists while the user is visiting that dialog, and which is visible to the elements of that dialog. Dialog variables are declared by <var> and <script> child elements of <form> and by the various form item elements. The child <var> and <script> elements of <form> are initialized when the form is first visited. The <var> elements inside executable content are initialized when the executable content is executed. The form item variables are initialized when the form item is collected. |
| (anonymous) | Each <block>, <filled>, and <catch> element defines a new anonymous scope to contain variables declared in that element. |
The following diagram shows the scope hierarchy:
Figure 11: The
scope hierarchy.
The curved arrows in this diagram show that each scope contains a pre-defined variable whose name is the same as the scope that refers to the scope itself. This allows you for example in the anonymous, dialog, and document scopes to refer to a variable X in the document scope using document.X. As another example, a <filled>'s variable scope is an anonymous scope local to the <filled>, whose parent variable scope is that of the <form>.
It is not recommended to use "session", "application", "document", and "dialog" as the names of variables and form items. While they are not reserved words, using them hides the pre-defined variables with the same name because of ECMAScript scoping rules used by VoiceXML.
Variables are referenced in cond and expr attributes:
<if cond="city == 'LA'"> <assign name="city" expr="'Los Angeles'"/> <elseif cond="city == 'Philly'"/> <assign name="city" expr="'Philadelphia'"/> <elseif cond="city =='Constantinople'"/> <assign name="city" expr="'Istanbul'"/> </if> <assign name="var1" expr="var1 + 1"/> <if cond="i > 1"> <assign name="i" expr="i-1"/> </if>
The expression language used in cond and expr is precisely ECMAScript. Note that the cond operators "<", "<=", and "&&" must be escaped in XML (to "<" and so on).
Variable references match the closest enclosing scope according to the scope chain given above. You can prefix a reference with a scope name for clarity or to resolve ambiguity. For instance to save the value of a form field item variable for use later on in a document:
<assign name="document.ssn" expr="dialog.ssn"/>
If the application root document has a variable x, it is referred to as application.x in non-root documents, and either application.x or document.x in the application root document. If the document does not have a specified application root and has a variable x, it is referred to as either application.x or document.x in the document.
Interpretations are sorted by confidence score, from highest to lowest. Interpretations with the same confidence score are further sorted according to the precedence relationship (see Section 3.1.4) among the grammars producing the interpretations. Different elements in application.lastresult$ will always differ in their utterance, interpretation, or both.
The number of application.lastresult$ elements is guaranteed to be greater than or equal to one and less than or equal to the system property "maxnbest". If no results have been generated by the system, then "application.lastresult$" shall be ECMAScript undefined.
Additionally, application.lastresult$ itself contains the properties confidence, utterance, inputmode, and interpretation corresponding to those of the 0th element in the ECMAScript array.
All of the shadow variables described above are set immediately after any recognition. In this context, a <nomatch> event counts as a recognition, and causes the value of "application.lastresult$" to be set, even though the existing values of field variables are not affected by a <nomatch>. In contrast, a <noinput> event does not change the value of "application.lastresult$". After the value of "application.lastresult$" is set, the value persists (unless it is modified by the application) until the browser enters the next waiting state, when it is set to undefined. Similarly, when an application root document is loaded, this variable is set to the value undefined. The variable application.lastresult$ and all of its components are writeable and can be modified by the application.
The following example shows how application.lastresult$ can be used in a field level <catch> to access a <link> grammar recognition result and transition to different dialog states depending on confidence:
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<link event="menulinkevent">
<grammar src="/grammars/linkgrammar.grxml" type="application/srgs+xml"/>
</link>
<form>
<field>
<prompt> Say something </prompt>
<catch event="menulinkevent">
<if cond="application.lastresult$.confidence < 0.7">
<goto nextitem="confirmlinkdialog"/>
<else/>
<goto next="./main_menu.html"/>
</if>
</catch>
</field>
</form>
</vxml>
The final example demonstrates how a script can be used to iterate over the array of results in application.lastresult$, where each element is represented by "application.lastresult$[i]":
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form>
<field name="color">
<prompt> Say a color </prompt>
<grammar type="application/srgs+xml" src="color.grxml" />
<filled>
<var name="confident_count" expr="0"/>
<script>
<![CDATA[
// number of results
var len = application.lastresult$.length;
// iterate through array
for (var i = 0; i < len; i++) {
// check if DTMF
if (application.lastresult$[i].confidence > .7) {
confident_count++;
}
}
]]>
</script>
<if cond="confident_count > 1">
<goto next="#verify"/>
</if>
</filled>
</field>
</form>
</vxml>
The platform throws events when the user does not respond, doesn't respond intelligibly, requests help, etc. The interpreter throws events if it finds a semantic error in a VoiceXML document, or when it encounters a <throw> element. Events are identified by character strings.
Each element in which an event can occur has a set of catch elements, which include:
<catch>
<error>
<help>
<noinput>
<nomatch>
An element inherits the catch elements ("as if by copy") from each of its ancestor elements, as needed. If a field, for example, does not contain a catch element for nomatch, but its form does, the form’s nomatch catch element is used. In this way, common event handling behavior can be specified at any level, and it applies to all descendents.
The "as if by copy" semantics for inheriting catch elements implies that when a catch element is executed, variables are resolved and thrown events are handled relative to the scope where the original event originated, not relative to the scope that contains the catch element. For example, consider a catch element that is defined at document scope handling an event that originated in a <field> within the document. In such a catch element variable references are resolved relative to the <field>'s scope, and if an event is thrown by the catch element it is handled relative to the <field>. Similarly, relative URI references in a catch element are resolved against the active document and not relative to the document in which they were declared. Finally, properties are resolved relative to the element where the event originated. For example, a prompt element defined as part of a document level catch would use the innermost property value of the active form item to resolve its timeout attribute if no value is explicitly specified.
The <throw> element throws an event. These can be the pre-defined ones:
<throw event="nomatch"/> <throw event="connection.disconnect.hangup"/>
or application-defined events:
<throw event="com.att.portal.machine"/>
Attributes of <throw> are:
| event | The event being thrown. |
|---|---|
| eventexpr | An ECMAScript expression evaluating to the name of the event being thrown. |
| message | A message string providing additional context about the event being
thrown. For the pre-defined events thrown by the platform, the value of
the message is platform-dependent. The message is available as the value of a variable within the scope of the catch element, see below. |
| messageexpr | An ECMAScript expression evaluating to the message string. |
Exactly one of "event" or "eventexpr" must be specified; otherwise, an error.badfetch event is thrown. Exactly one of "message" or "messageexpr" may be specified; otherwise, an error.badfetch event is thrown.
Unless explicited stated otherwise, VoiceXML does not specify when events are thrown.
The catch element associates a catch with a document, dialog, or form item. It contains executable content.
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="launch_missiles">
<field name="user_id" type="digits">
<prompt>What is your username</prompt>
</field>
<field name="password">
<prompt>What is the code word?</prompt>
<grammar version="1.0" root="root">
<rule id="root" scope="public">rutabaga</rule>
</grammar>
<help>It is the name of an obscure vegetable.</help>
<catch event="nomatch noinput" count="3">
<prompt>Security violation!</prompt>
<submit next="http://www.example.com/apprehend_felon.vxml"
namelist="user_id"/>
</catch>
</field>
</form>
</vxml>
The catch element's anonymous variable scope includes the special variable _event which contains the name of the event that was thrown. For example, the following catch element can handle two types of events:
<catch event="event.foo event.bar">
<if cond="_event=='event.foo'">
<!-- Play this for event.foo events -->
<audio src="foo.wav"/>
<else/>
<!-- Play this for event.bar events -->
<audio src="bar.wav"/>
</if>
<!-- Continue with common handling for either event -->
</catch>
The _event variable is inspected to select the audio to play based on the event that was thrown. The foo.wav file will be played for event.foo events. The bar.wav file will be played for event.bar events. The remainder of the catch element contains executable content that is common to the handling of both event types.
The catch element's anonymous variable scope also includes the special variable _message which contains the value of the message string from the corresponding <throw> element, or a platform-dependent value for the pre-defined events raised by the platform. If the thrown event does not specify a message, the value of _message is ECMAScript undefined.
If a <catch> element contains a <throw> element with the same event, then there may be an infinite loop:
<catch event="help"> <throw event="help"/> </catch>
A platform could detect this situation and throw a semantic error instead.
Attributes of <catch> are:
| event | The event or events to catch. A space-separated list of events may be specified, indicating that this <catch> element catches all the events named in the list. In such a case a separate event counter (see "count" attribute) is maintained for each event. If the attribute is unspecified, all events are to be caught. |
|---|---|
| count | The occurrence of the event (default is 1). The count allows you to
handle different occurrences of the same event differently.
Each <form>, <menu>, and form item maintains a counter for each event that occurs while it is being visited. Item-level event counters are used for events thrown while visiting individual form items and while executing <filled> elements contained within those items. Form-level and menu-level counters are used for events thrown during dialog initialization and while executing form-level <filled> elements. Form-level and menu-level event counters are reset each time the <menu> or <form> is re-entered. Form-level and menu-level event counters are not reset by the <clear> element. Item-level event counters are reset each time the <form> containing the item is re-entered. Item-level event counters are also reset when the item is reset with the <clear> element. An item's event counters are not reset when the item is re-entered without leaving the <form>." Counters are incremented against the full event name and every prefix matching event name; for example, occurrence of the event "event.foo.1" increments the counters for "event.foo.1" plus "event.foo" and "event". |
| cond | An expression which must evaluate to true after conversion to boolean in order for the event to be caught. Defaults to true. |
The <error>, <help>, <noinput>, and <nomatch> elements are shorthands for very common types of <catch> elements.
The <error> element is short for <catch event="error"> and catches all events of type error:
<error> An error has occurred -- please call again later. <exit/> </error>
The <help> element is an abbreviation for <catch event="help">:
<help>No help is available.</help>
The <noinput> element abbreviates <catch event="noinput">:
<noinput>I didn't hear anything, please try again.</noinput>
And the <nomatch> element is short for <catch event="nomatch">:
<nomatch>I heard something, but it wasn't a known city.</nomatch>
These elements take the attributes:
| count | The event count (as in <catch>). |
|---|---|
| cond | An optional condition to test to see if the event is caught by this element (as in <catch> described in Section 5.2.2). Defaults to true. |
An element inherits the catch elements ("as if by copy") from each of its ancestor elements, as needed. For example, if a <field> element inherits a <catch> element from the document
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<catch event="event.foo">
<audio src="beep.wav"/>
</catch>
<form>
<field name="color">
<prompt>Please say a primary color</prompt>
<grammar type="application/srgs">red | yellow | blue</grammar>
<nomatch>
<throw event="event.foo"/>
</nomatch>
</field>
</form>
</vxml>
then the <catch> element is implicitly copied into <field> as if defined below:
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form>
<field>
<prompt>Please say a primary color</prompt>
<grammar type="application/srgs">red | yellow | blue</grammar>
<nomatch>
<throw event="event.foo"/>
</nomatch>
<catch event="event.foo">
<audio src="beep.wav"/>
</catch>
</field>
</form>
</vxml>
When an event is thrown, the scope in which the event is handled and its enclosing scopes are examined to find the best qualified catch element, according to the following algorithm:
The name of a thrown event matches the catch element event name if it is an exact match, a prefix match or the catch event name is not specified. A prefix match occurs when the catch element event attribute is a token prefix of the name of the event being thrown, where the dot is the token separator, all trailing dots are removed, and the empty string matches everything. For example,
<catch event="connection.disconnect"> <prompt>Caught a connection dot disconnect event</prompt> </catch>
will prefix match the event connection.disconnect.transfer.
<catch event="com.example.myevent"> <prompt>Caught a com dot example dot my event</prompt> </catch>
prefix matches com.example.myevent.event1., com.example.myevent. and com.example.myevent..event1 but not com.example.myevents.event1. Finally,
<catch event="."> <prompt>Caught an event</prompt> </catch>
prefix matches all events (as does <catch> without an event attribute).
Note that the catch element selection algorithm gives priority to catch elements that occur earlier in a document over those that occur later, but does not give priority to catch elements that are more specific over those that are less specific. Therefore is generally advisable to specify catch elements in order from more specific to less specific. For example, it would be advisable to specify catch elements for "error.foo" and "error" in that order, as follows:
<catch event="error.foo"> <prompt>Caught an error dot foo event</prompt> </catch> <catch event="error"> <prompt>Caught an error event</prompt> </catch>
If the catch elements were specified in the opposite order, the catch element for "error.foo" would never be executed.
The interpreter is expected to provide implicit default catch handlers for the noinput, help, nomatch, cancel, exit, and error events if the author did not specify them.
The system default behavior of catch handlers for various events and errors is summarized by the definitions below that specify (1) whether any audio response is to be provided, and (2) how execution is affected. Note: where an audio response is provided, the actual content is platform dependent.
| Event Type | Audio Provided | Action |
|---|---|---|
| cancel | no | don’t reprompt |
| error | yes | exit interpreter |
| exit | no | exit interpreter |
| help | yes | reprompt |
| noinput | no | reprompt |
| nomatch | yes | reprompt |
| maxspeechtimeout | yes | reprompt |
| connection.disconnect | no | exit interpreter |
| all others | yes | exit interpreter |
Specific platforms will differ in the default prompts presented.
There are pre-defined events, and application and platform-specific events. Events are also subdivided into plain events (things that happen normally), and error events (abnormal occurrences). The error naming convention allows for multiple levels of granularity.
A conforming browser may throw an event that extends a pre-defined event string so long as the event contains the specified pre-defined event string as a dot-separated exact initial substring of its event name. Applications that write catch handlers for the pre-defined events will be interoperable. Applications that write catch handlers for extended event names are not guaranteed interoperability. For example, if in loading a grammar file a syntax error is detected the platform must throw "error.badfetch". Throwing "error.badfetch.grammar.syntax" is an acceptable implementation.
Further information about an event may be specified in the "_message" variable (see Section 5.2.2).
The pre-defined events are:
In addition to transfer errors (Section 2.3.7.3), the pre-defined errors are:
Errors encountered during document loading, including transport errors (no document found, HTTP status code 404, and so on) and syntactic errors (no <vxml> element, etc) result in a badfetch error event raised in the calling document. Errors that occur after loading and before entering the initialization phase of the Form Interpretation Algorithm are handled in a platform-specific manner. Errors that occur after entering the FIA initialization phase, such as semantic errors, are raised in the new document. The handling of errors encountered during the loading of the first document in a session is platform-specific.
Application-specific and platform-specific event types should use the reversed Internet domain name convention to avoid naming conflicts. For example:
Catches can catch specific events (cancel) or all those sharing a prefix (error.unsupported).
Executable content refers to a block of procedural logic. Such logic appears in:
The <block> form item.
The <filled> actions in forms and input items.
Event handlers (<catch>, <help>, et cetera).
Executable elements are executed in document order in their block of procedural logic. If an executable element generates an error, that error is thrown immediately. Subsequent executable elements in that block of procedural logic are not executed.
This section covers the elements that can occur in executable content.
This element declares a variable. It can occur in executable content or as a child of <form> or <vxml>. Examples:
<var name="phone" expr="'6305551212'"/> <var name="y" expr="document.z+1"/>
If it occurs in executable content, it declares a variable in the anonymous scope associated with the enclosing <block>, <filled>, or catch element. This declaration is made only when the <var> element is executed. If the variable is already declared in this scope, subsequent declarations act as assignments, as in ECMAScript.
If a <var> is a child of a <form> element, it declares a variable in the dialog scope of the <form>. This declaration is made during the form’s initialization phase as described in Section 2.1.6.1. The <var> element is not a form item, and so is not visited by the Form Interpretation Algorithm’s main loop.
If a <var> is a child of a <vxml> element, it declares a variable in the document scope; and if it is the child of a <vxml> element in a root document then it also declares the variable in the application scope. This declaration is made when the document is initialized; initializations happen in document order.
Attributes of <var> include:
| name | The name of the variable that will hold the result. |
|---|---|
| expr | The initial value of the variable (optional). If there is no expr attribute, the variable retains its current value, if any. Variables start out with the ECMAScript value undefined if they are not given initial values. |
The <assign> element assigns a value to a variable:
<assign name="flavor" expr="'chocolate'"/> <assign name="document.mycost" expr="document.mycost+14"/>
It is illegal to make an assignment to a variable that has not been explicitly declared using a <var> element or a var statement within a <script>. Attempting to assign to an undeclared variable causes an error.semantic event to be thrown.
Note that when an ECMAScript object, e.g. "obj", has been properly initialized then its properties, for instance "obj.prop1", can be assigned without explicit declaration (in fact, an attempt to declare ECMAScript object properties such as "obj.prop1" would result in an error.semantic event being thrown).
Attributes include:
| name | The name of the variable being assigned to. |
|---|---|
| expr | The new value of the variable. |
The <clear> element resets one or more variables, including form items. Resetting form items includes:
Setting the form item variable to ECMAScript undefined.
Reinitializing the prompt counter and the event counters for the form item.
For example:
<clear namelist="city state zip"/>
The attribute is:
| namelist | The list of variables to be reset; this can include variable names other than form items. When not specified, all form items in the current form are cleared. |
|---|
The <if> element is used for conditional logic. It has optional <else> and <elseif> elements.
<if cond="total > 1000"> <prompt>This is way too much to spend.</prompt> <throw event="com.xyzcorp.acct.toomuchspent"/> </if> <if cond="amount < 29.95"> <assign name="x" expr="amount"/> <else/> <assign name="x" expr="29.95"/> </if> <if cond="flavor == 'vanilla'"> <assign name="flavor_code" expr="'v'"/> <elseif cond="flavor == 'chocolate'"/> <assign name="flavor_code" expr="'h'"/> <elseif cond="flavor == 'strawberry'"/> <assign name="flavor_code" expr="'b'"/> <else/> <assign name="flavor_code" expr="'?'"/> </if>
Prompts can appear in executable content, in their full generality, except that the <prompt> count attribute is meaningless. In particular, the cond attribute can be used in executable content. Prompts may be wrapped with <prompt> and </prompt>, or represented using PCDATA. Wherever <prompt> is allowed, the PCDATA xyz is interpreted exactly as if it had appeared as <prompt>xyz</prompt>.
<nomatch count="1">
To open the pod bay door, say your code phrase clearly.
</nomatch>
<nomatch count="2">
<prompt>
This is your <emphasis>last</emphasis> chance.
</prompt>
</nomatch>
<nomatch count="3">
Entrance denied.
<exit/>
</nomatch>
The FIA expects a catch element to queue appropriate prompts in the course of handling an event. Therefore, the FIA does not generally perform the normal selection and queuing of prompts on the next iteration following the execution of a catch element. However, the FIA does perform normal selection and queueing of prompts after the execution of a catch element (<catch>, <error>, <help>, <noinput>, <nomatch>) in two cases:
In these two cases, after the FIA selects the next form item to visit, it performs normal prompt processing, including selecting and queuing the form item's prompts and incrementing the form item's prompt counter.
For example, this noinput catch expects the next form item prompt to be selected and played:
<field name="want_ice_cream">
<grammar type="application/srgs+xml" src="/grammars/boolean.grxml"/>
<prompt>Do you want ice cream for dessert?</prompt>
<prompt count="2">
If you want ice cream, say yes.
If you do not want ice cream, say no.
</prompt>
<noinput>
I could not hear you.
<!-- Cause the next prompt to be selected and played. -->
<reprompt/>
</noinput>
</field>
A quiet user would hear:
C: Do you want ice cream for dessert?
H: (silence)
C: I could not hear you.
C: If you want ice cream, say yes. If you don’t want ice cream, say no.
H: (silence)
C: I could not hear you.
C: If you want ice cream, say yes. If you don’t want ice cream, say no.
H: No
If there were no <reprompt>, the user would instead hear:
C: Do you want ice cream for dessert?
H: (silence)
C: I could not hear you.
H: (silence)
C: I could not hear you.
H: No
Note that a consequence of skipping the prompt selection phase as described above is that the prompt counter of the form item selected by the FIA after the execution of a catch element (that does not execute a <reprompt>, or leave the dialog via <goto>, <submit> or <return>) will not be incremented.
Also note that the prompt selection phase following the execution of a catch element (that does not execute a <reprompt> or leave the dialog via <goto>, <submit> or <return>) is skipped even if the form item selected by the FIA is different from the previous form item.
The <reprompt> element has no effect outside of a catch.
The <goto> element is used to:
transition to another form item in the current form,
transition to another dialog in the current document, or
transition to another document.
To transition to another form item, use the nextitem attribute, or the expritem attribute if the form item name is computed using an ECMAScript expression:
<goto nextitem="ssn_confirm"/> <goto expritem="(type==12)? 'ssn_confirm' : 'reject'"/>
To go to another dialog in the same document, use next (or expr) with only a URI fragment:
<goto next="#another_dialog"/> <goto expr="'#' + 'another_dialog'"/>
To transition to another document, use next (or expr) with a URI:
<goto next="http://flight.example.com/reserve_seat"/> <goto next="./special_lunch#wants_vegan"/>
The URI may be absolute or relative to the current document. You may specify the starting dialog in the next document using a fragment that corresponds to the value of the id attribute of a dialog. If no fragment is specified, the first dialog in that document is chosen.
Note that transitioning to another dialog in the current document causes the old dialog’s variables to be lost, even in the case where a dialog is transitioning to itself. Transitioning to another document using an absolute or relative URI will likewise drop the old document level variables, even if the new document is the same one that is making the transition. However, document variables are retained when transitioning to an empty URI reference with a fragment identifier. For example, the following statements behave differently in a document with the URI http://someco.example.com/index.vxml:
<goto next="#foo"/> <goto next="http://someco.example.com/index.vxml#foo"/>
According to [RFC2396], the fragment identifier (the part after the '#') is not part of a URI and transitioning to empty URI references plus fragment identifiers should never result in a new document fetch. Therefore "#foo" in the first statement is an empty URI reference with a fragment identifier and document variables are retained. In the second statement "#foo" is part of an absolute URI and the document variables are lost. If you want data to persist across multiple documents, store data in the application scope.
The dialog to transition to is specified by the URI reference in the <goto>'s next or expr attribute (see [RFC2396]). If this URI reference contains an absolute or relative URI, which may include a query string, then that URI is fetched and the dialog is found in the resulting document.
If the URI reference contains only a fragment (i.e., no absolute or relative URI), then there is no fetch: the dialog is found in the current document.
The URI reference's fragment, if any, names the dialog to transition to. When there is no fragment, the dialog chosen is the lexically first dialog in the document.
If the form item, dialog or document to transition to is not valid (i.e. the form item, dialog or document does not exist), an error.badfetch must be thrown. Note that for errors which occur during a dialog or document transition, the scope in which errors are handled is platform specific. For errors which occur during form item transition, the event is handled in the dialog scope.
Attributes of <goto> are:
| next | The URI to which to transition. |
|---|---|
| expr | An ECMAScript expression that yields the URI. |
| nextitem | The name of the next form item to visit in the current form. |
| expritem | An ECMAScript expression that yields the name of the next form item to visit. |
| fetchaudio | See Section 6.1. This defaults to the fetchaudio property. |
| fetchhint | See Section 6.1. This defaults to the documentfetchhint property. |
| fetchtimeout | See Section 6.1. This defaults to the fetchtimeout property. |
| maxage | See Section 6.1. This defaults to the documentmaxage property. |
| maxstale | See Section 6.1. This defaults to the documentmaxstale property. |
Exactly one of "next", "expr", "nextitem" or "expritem" must be specified; otherwise, an error.badfetch event is thrown.
The <submit> element is used to submit information to the origin web server and then transition to the document sent back in the response. Unlike <goto>, it lets you submit a list of variables to the document server via an HTTP GET or POST request. For example, to submit a set of form items to the server you might have:
<submit next="log_request" method="post" namelist="name rank serial_number" fetchtimeout="100s" fetchaudio="audio/brahms2.wav"/>
The dialog to transition to is specified by the URI reference in the <submit>'s next or expr attribute (see [RFC2396], Section 4.2). The URI is always fetched even if it contains just a fragment. In the case of a fragment, the URI requested is the base URI of the current document. This means that the following two elements have substantially different effects:
<goto next="#get_pin"/> <submit next="#get_pin"/>
Note that although the URI is always fetched and the resulting document is transitioned to, some <submit> requests can be satisfied by intermediate caches. This might happen, for example, if the origin web server provides an explicit expiration time with the response.
If the dialog or document to transition to is not valid (i.e. the dialog or document does not exist), an error.badfetch must be thrown. Note that for errors which occur during a dialog or document transition, the scope in which errors are handled is platform specific.
Attributes of <submit> include:
| next | The URI reference. |
|---|---|
| expr | Like next, except that the URI reference is dynamically determined by evaluating the given ECMAScript expression. |
| namelist | The list of variables to submit. By default, all the named input item variables are submitted. If a namelist is supplied, it may contain individual variable references which are submitted with the same qualification used in the namelist. Declared VoiceXML and ECMAScript variables can be referenced. |
| method | The request method: get (the default) or post. |
| enctype | The media encoding type of the submitted document. The default is application/x-www-form-urlencoded. Interpreters must also support multipart/form-data and may support additional encoding types. |
| fetchaudio | See Section 6.1. This defaults to the fetchaudio property. |
| fetchhint | See Section 6.1. This defaults to the documentfetchhint property. |
| fetchtimeout | See Section 6.1. This defaults to the fetchtimeout property. |
| maxage | See Section 6.1. This defaults to the documentmaxage property. |
| maxstale | See Section 6.1. This defaults to the documentmaxstale property. |
Exactly one of "next" or "expr" must be specified; otherwise, an error.badfetch event is thrown.
When an ECMAScript variable is submitted to the server its value is first converted into a string before being submitted. If the variable is an ECMAScript Object the mechanism by which it is submitted is not currently defined. The mechanism of ECMAScript Object submission is reserved for future definition. Instead of submitting ECMAScript Objects directly, the application developer may explicitly submit properties of Object as in "date.month date.year".
If a <submit> contains a variable which references recorded audio but does not contain an ENCTYPE of multipart/form-data, the behavior is not specified. It is probably inappropriate to attempt to URL-encode large quantities of data.
Returns control to the interpreter context which determines what to do next.
<exit/>
This element differs from <return> in that it terminates all loaded documents, while <return> returns from a <subdialog> invocation. If the <subdialog> caused a new document (or application) to be invoked, then <return> will cause that document to be terminated, but execution will resume after the <subdialog>.
Note that once <exit> returns control to the interpreter context, the interpreter context is free to do as it wishes. It may play a top level menu for the user, drop the call, or transfer the user to an operator, for example.
Attributes include:
| expr | An ECMAScript expression that is evaluated as the return value (e.g. "0", "'oops!'", or "field1"). |
|---|---|
| namelist | Variable names to be returned to interpreter context. The default is to return no variables; this means the interpreter context will receive an empty ECMAScript object. |
Exactly one of "expr" or "namelist" may be specified; otherwise, an error.badfetch event is thrown.
The <exit> element does not throw an "exit" event.
Return ends execution of a subdialog and returns control and data to a calling dialog.
The attributes are:
| event | Return, then throw this event. |
|---|---|
| eventexpr | Return, then throw the event to which this ECMAScript expression evaluates. |
| message | A message string providing additional context about the event being thrown. The message is available as the value of a variable within the scope of the catch element, see Section 5.2.2. |
| messageexpr | An ECMAScript expression evaluating to the message string. |
| namelist | Variable names to be returned to calling dialog. The default is to return no variables; this means the caller will receive an empty ECMAScript object. |
Exactly one of "event", "eventexpr" or "namelist" may be specified; otherwise, an error.badfetch event is thrown. Exactly one of "message" or "messageexpr" may be specified; otherwise, an error.badfetch event is thrown.
In returning from a subdialog, an event can be thrown at the invocation point, or data is returned as an ECMAScript object with properties corresponding to the variable specified in its namelist. A return element that is encountered when not executing as a subdialog throws a semantic error.
The example below shows an event propagated from a subdialog to its calling dialog when the subdialog fails to obtain a recognizable result. It also shows data returned under normal conditions.
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form>
<subdialog name="result" src="#getssn">
<nomatch>
<!-- a no match event that is returned by the
subdialog indicates that a valid social security
number could not be matched. -->
<goto next="http://myservice.example.com/ssn-problems.vxml"/>
</nomatch>
<filled>
<submit namelist="result.ssn"
next="http://myservice.example.com/cgi-bin/process"/>
</filled>
</subdialog>
</form>
<form id="getssn">
<field name="ssn">
<grammar src="http://grammarlib/ssn.grxml"
type="application/srgs+xml"/>
<prompt> Please say social security number.</prompt>
<nomatch count="3">
<return event="nomatch"/>
</nomatch>
<filled>
<return namelist="ssn"/>
</filled>
</field>
</form>
</vxml>
The subdialog event handler for <nomatch> is triggered on the third failure to match; when triggered, it returns from the subdialog, and includes the nomatch event to be thrown in the context of the calling dialog. In this case, the calling dialog will execute its <nomatch> handler, rather than the <filled> element, where the resulting action is to execute a <goto> element. Under normal conditions, the <filled> element of the subdialog is executed after a recognized social security number is obtained, and then this value is returned to the calling dialog, and is accessible as result.ssn.
Causes the interpreter context to disconnect from the user. As a result, the interpreter context will throw a connection.disconnect.hangup event, which may be caught to do cleanup processing, e.g.
<disconnect/>
The <script> element allows the specification of a block of client-side scripting language code, and is analogous to the [HTML] <SCRIPT> element. For example, this document has a script that computes a factorial.
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<script> <![CDATA[
function factorial(n)
{
return (n <= 1)? 1 : n * factorial(n-1);
}
]]> </script>
<form id="form">
<field name="fact">
<grammar type="application/srgs+xml" src="/grammars/number.grxml"/>
<prompt>
Tell me a number and I'll tell you its factorial.
</prompt>
<filled>
<prompt>
<value expr="fact"/> factorial is
<value expr="factorial(fact)"/>
</prompt>
</filled>
</field>
</form>
</vxml>
A <script> element may occur in the <vxml> and <form> elements, or in executable content (in <filled>, <if>, <block>, <catch>, or the short forms of <catch>). Scripts in the <vxml> element are evaluated just after the document is loaded, along with the <var> elements, in document order. Scripts in the <form> element are evaluated in document order, along with <var> elements and form item variables, each time execution moves into the <form> element. A <script> element in executable content is executed, like other executable elements, as it is encountered.
The <script> element has the following attributes:
| src | The URI specifying the location of the script, if it is external. |
|---|---|
| charset | The character encoding of the script designated by src. UTF-8 and UTF-16 encodings of ISO/IEC 10646 must be supported (as in [XML]) and other encodings, as defined in the [IANA], may be supported. The default value is UTF-8. |
| fetchhint | See Section 6.1. This defaults to the scriptfetchhint property. |
| fetchtimeout | See Section 6.1. This defaults to the fetchtimeout property. |
| maxage | See Section 6.1. This defaults to the scriptmaxage property. |
| maxstale | See Section 6.1. This defaults to the scriptmaxstale property. |
Either an "src" attribute or an inline script (but not both) must be specified; otherwise, an error.badfetch event is thrown.
The VoiceXML <script> element (unlike the [HTML] <SCRIPT> element) does not have a type attribute; ECMAScript is the required scripting language for VoiceXML.
Each <script> element is executed in the scope of its containing element; i.e., it does not have its own scope. This means for example that variables declared with var in the <script> element are declared in the scope of the containing element of the <script> element. (In ECMAScript terminology, the "variable object" becomes the current scope of the containing element of the <script> element).
Here is a time-telling service with a block containing a script that initializes time variables in the dialog scope of a form:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form>
<var name="hours"/>
<var name="minutes"/>
<var name="seconds"/>
<block>
<script>
var d = new Date();
hours = d.getHours();
minutes = d.getMinutes();
seconds = d.getSeconds();
</script>
</block>
<field name="hear_another">
<grammar type="application/srgs+xml" src="/grammars/boolean.grxml"/>
<prompt>
The time is <value expr="hours"/> hours,
<value expr="minutes"/> minutes, and
<value expr="seconds"/> seconds.
</prompt>
<prompt>Do you want to hear another time?</prompt>
<filled>
<if cond="hear_another">
<clear/>
</if>
</filled>
</field>
</form>
</vxml>
The content of a <script> element is evaluated in the same scope as a <var> element (see 5.1.2 Variable Scopes and 5.3.1 VAR).
The ECMAScript scope chain (see section 10.1.4 in [ECMASCRIPT]) is set up so that variables declared either with <var> or inside <script> are put into the scope associated with the element in which the <var> or <script> element occurs. For example, the variable declared in a <script> element under a <form> element has a dialog scope, and can be accessed as a dialog scope variable as follows:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form>
<script>
var now = new Date(); <!-- this has a dialog scope-->
</script>
<var name="seconds" expr="now.getSeconds()"/> <!-- this has a dialog scope-->
<block>
<var name="now" expr="new Date()"/> <!-- this has an anonymous scope -->
<script>
var current = now.getSeconds(); <!-- "now" in the anonymous scope -->
var approx = dialog.now.getSeconds(); <!-- "now" in the dialog scope -->
</script>
</block>
</form>
</vxml>
All variables must be declared before being referenced by ECMAScript scripts, or by VoiceXML elements as described in Section 5.1.1.
The <log> element allows an application to generate a logging or debug message which a developer can use to help in application development or post-execution analysis of application performance.
The <log> element may contain any combination of text (CDATA) and <value> elements. The generated message consists of the concatenation of the text and the string form of the value of the "expr" attribute of the <value> elements.
The manner in which the message is displayed or logged is platform-dependent. The usage of label is platform-dependent. Platforms are not required to preserve white space.
ECMAScript expressions in <log> must be evaluated in document order. The use of the <log> element should have no other side-effects on interpretation.
<log>The card number was <value expr="card_num"/></log>
The <log> element has the following attributes:
| label | A string which may be used, for example, to indicate the purpose of the log. |
|---|---|
| expr | An ECMAscript expression evaluating to a string. |
A VoiceXML interpreter context needs to fetch VoiceXML documents, and other resources, such as audio files, grammars, scripts, and objects. Each fetch of the content associated with a URI is governed by the following attributes:
| fetchtimeout | The interval to wait for the content to be returned before throwing an error.badfetch event. The value is a Time Designation (see Section 6.5). If not specified, a value derived from the innermost fetchtimeout property is used. |
|---|---|
| fetchhint | Defines when the interpreter context should retrieve content from the server. prefetch indicates a file may be downloaded when the page is loaded, whereas safe indicates a file that should only be downloaded when actually needed. If not specified, a value derived from the innermost relevant fetchhint property is used. |
| maxage | Indicates that the document is willing to use content whose age is no greater than the specified time in seconds (cf. 'max-age' in HTTP 1.1 [RFC2616]). The document is not willing to use stale content, unless maxstale is also provided. If not specified, a value derived from the innermost relevant maxage property, if present, is used. |
| maxstale | Indicates that the document is willing to use content that has exceeded its expiration time (cf. 'max-stale' in HTTP 1.1 [RFC2616]). If maxstale is assigned a value, then the document is willing to accept content that has exceeded its expiration time by no more than the specified number of seconds. If not specified, a value derived from the innermost relevant maxstale property, if present, is used. |
When content is fetched from a URI, the fetchtimeout attribute determines how long to wait for the content (starting from the time when the resource is needed), and the fetchhint attribute determines when the content is fetched. The caching policy for a VoiceXML interpreter context utilizes the maxage and maxstale attributes and is explained in more detail below.
The fetchhint attribute, in combination with the various fetchhint properties, is merely a hint to the interpreter context about when it may schedule the fetch of a resource. Telling the interpreter context that it may prefetch a resource does not require that the resource be prefetched; it only suggests that the resource may be prefetched. However, the interpreter context is always required to honor the safe fetchhint.
When transitioning from one dialog to another, through either a <subdialog>, <goto>, <submit>, <link>, or <choice> element, there are additional rules that affect interpreter behavior. If the referenced URI names a document (e.g. "doc#dialog"), or if query data is provided (through POST or GET), then a new document is obtained (either from a local cache, intermediate cache, or from a origin web server). When it is obtained, the document goes through its initialization phase (i.e., obtaining and initializing a new application root document if needed, initializing document variables, and executing document scripts). The requested dialog (or first dialog if none is specified) is then initialized and execution of the dialog begins.
Generally, if a URI reference contains only a fragment (e.g., "#my_dialog"), then no document is fetched, and no initialization of that document is performed. However, <submit> always results in a fetch, and if a fragment is accompanied by a namelist attribute there will also be a fetch.
Another exception is when a URI reference in a leaf document references the application root document. In this case, the root document is transitioned to without fetching and without initialization even if the URI reference contains an absolute or relative URI (see Section 1.5.2 and [RFC2396]). However, if the URI reference to the root document contains a query string or a namelist attribute, the root document is fetched.
Elements that fetch VoiceXML documents also support the following additional attribute:
| fetchaudio | The URI of the audio clip to play while the fetch is being done. If not specified, the fetchaudio property is used, and if that property is not set, no audio is played during the fetch. The fetching of the audio clip is governed by the audiofetchhint, audiomaxage, audiomaxstale, and fetchtimeout properties in effect at the time of the fetch. The playing of the audio clip is governed by the fetchaudiodelay, and fetchaudiominimum properties in effect at the time of the fetch. |
|---|
The fetchaudio attribute is useful for enhancing a user experience when there may be noticeable delays while the next document is retrieved. This can be used to play background music, or a series of announcements. When the document is retrieved, the audio file is interrupted if it is still playing. If an error occurs retrieving fetchaudio from its URI, no badfetch event is thrown and no audio is played during the fetch.
The VoiceXML interpreter context, like [HTML] visual browsers, can use caching to improve performance in fetching documents and other resources; audio recordings (which can be quite large) are as common to VoiceXML documents as images are to HTML pages. In a visual browser it is common to include end user controls to update or refresh content that is perceived to be stale. This is not the case for the VoiceXML interpreter context, since it lacks equivalent end user controls. Thus enforcement of cache refresh is at the discretion of the document through appropriate use of the maxage, and maxstale attributes.
The caching policy used by the VoiceXML interpreter context must adhere to the cache correctness rules of HTTP 1.1 ([RFC2616]). In particular, the Expires and Cache-Control headers must be honored. The following algorithm summarizes these rules and represents the interpreter context behavior when requesting a resource:
The "maxstale check" is:
Note: it is an optimization to perform a "get if modified" on a document still present in the cache when the policy requires a fetch from the server.
While the maxage and maxstale attributes are drawn from and directly supported by HTTP 1.1, some resources may be addressed by URIs that name protocols other than HTTP. If the protocol does not support the notion of resource age, the interpreter context shall compute a resource's age from the time it was received. If the protocol does not support the notion of resource staleness, the interpreter context shall consider the resource to have expired immediately upon receipt.
VoiceXML allows the author to control the caching policy for each use of each resource (except for any document referenced by the <vxml> element's application attribute: there is no markup mechanism to control the caching policy for an application root document).
Each resource-related element may specify maxage and maxstale attributes. Setting maxage to a non-zero value can be used to get a fresh copy of a resource that may not have yet expired in the cache. A fresh copy can be unconditionally requested by setting maxage to zero.
Using maxstale enables the author to state that an expired copy of a resource, that is not too stale (according to the rules of HTTP 1.1), may be used. This can improve performance by eliminating a fetch that would otherwise be required to get a fresh copy. It is especially useful for authors who may not have direct server-side control of the expiration dates of large static files.
Prefetching is an optional feature that an interpreter context may implement to obtain a resource before it is needed. A resource that may be prefetched is identified by an element whose fetchhint attribute equals "prefetch". When an interpreter context does prefetch a resource, it must ensure that the resource fetched is precisely the one needed. In particular, if the URI is computed with an expr attribute, the interpreter context must not move the fetch up before any assignments to the expression's variables. Likewise, the fetch for a <submit> must not be moved prior to any assignments of the namelist variables.
The expiration status of a resource must be checked on each use of the resource, and, if its fetchhint attribute is "prefetch", then it is prefetched. The check must follow the caching policy specified in Section 6.1.2.
The "http" URI protocol must be supported by VoiceXML platforms, the "https" protocol should be supported and other URI protocols may be supported.
Metadata information is information about the document rather than the document's content. VoiceXML 2.0 provides two elements in which metadata information can be expressed: <meta> and <metadata>. The <metadata> element provides more general and powerful treatment of metadata information than <meta>.
VoiceXML does not specify required metadata information. However, it does recommend that metadata is expressed using the <metadata> element with information in Resource Description Framework (RDF) [RDF-SYNTAX] using the Dublin Core version 1.0 RDF schema [DC] (see Section 6.2.2).
The <meta> element specifies meta information as in [HTML]. There are two types of <meta>.
The first type specifies a metadata property of the document as a whole and is expressed by the pair of attributes, name and content. For example to specify the maintainer of a VoiceXML document:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<meta name="maintainer" content="jpdoe@anycompany.example.com"/>
<form>
<block>
<prompt>Hello</prompt>
</block>
</form>
</vxml>
The second type of <meta> specifies HTTP response headers and is expressed by the pair of attributes http-equiv and content. In the following example, the first <meta> element sets an expiration date that prevents caching of the document; the second <meta> element sets the Date header.
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<meta http-equiv="Expires" content="0"/>
<meta http-equiv="Date" content="Thu, 12 Dec 2000 23:27:21 GMT"/>
<form>
<block>
<prompt>Hello</prompt>
</block>
</form>
</vxml>
Attributes of <meta> are:
| name | The name of the metadata property. |
|---|---|
| content | The value of the metadata property. |
| http-equiv | The name of an HTTP response header. |
Exactly one of "name" or "http-equiv" must be specified; otherwise, an error.badfetch event is thrown.
The <metadata> element is container in which information about the document can be placed using a metadata schema. Although any metadata schema can be used with <metadata>, it is recommended that the RDF schema is used in conjunction with metadata properties defined in the Dublin Core Metadata Initiative.
RDF is a declarative language and provides a standard way for using XML to represent metadata in the form of statements about properties and relationships of items on the Web. Content creators should refer to W3C metadata Recommendations [RDF-SYNTAX] and [RDF-SCHEMA] as well as the Dublin Core Metadata Initiative [DC], which is a set of generally applicable core metadata properties (e.g., Title, Creator, Subject, Description, Copyrights, etc.).
The following Dublin Core metadata properties are recommended in <metadata>:
| Creator | An entity primarily responsible for making the content of the resource. |
|---|---|
| Rights | Information about rights held in and over the resource. |
| Subject | The topic of the content of the resource. Typically, a subject will be expressed as keywords, key phrases or classification codes. Recommended best practice is to select values from a controlled vocabulary or formal classification scheme. |
Here is an example of how <metadata> can be included in a VoiceXML document using the Dublin Core version 1.0 RDF schema [DC]:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<metadata>
<rdf:RDF
xmlns:rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:rdfs = "http://www.w3.org/TR/1999/PR-rdf-schema-19990303#"
xmlns:dc = "http://purl.org/metadata/dublin_core#">
<!-- Metadata about the VoiceXML document -->
<rdf:Description about="http://www.example.com/meta.vxml"
dc:Title="Directory Enquiry Service"
dc:Description="Directory Enquiry Service for London in VoiceXML"
dc:Publisher="W3C"
dc:Language="en"
dc:Date="2002-02-12"
dc:Rights="Copyright 2002 John Smith"
dc:Format="application/voicexml+xml" >
<dc:Creator>
<rdf:Seq ID="CreatorsAlphabeticalBySurname">
<rdf:li>Jackie Crystal</rdf:li>
<rdf:li>William Lee</rdf:li>
</rdf:Seq>
</dc:Creator>
</rdf:Description>
</rdf:RDF>
</metadata>
<form>
<block>
<prompt>Hello</prompt>
</block>
</form>
</vxml>
The <property> element sets a property value. Properties are used to set values that affect platform behavior, such as the recognition process, timeouts, caching policy, etc.
Properties may be defined for the whole application, for the whole document at the <vxml> level, for a particular dialog at the <form> or <menu> level, or for a particular field item. Properties apply to their parent element and all the descendants of the parent. A property at a lower level overrides a property at a higher level. When different values for a property are specified at the same level, the last one in document order applies. Properties specified in the application root document provide default values for properties in every document in the application; properties specified in an individual document override property values specified in the application root document.
If a platform detects that the value of a property is invalid, then it should throw an error.semantic.
In some cases, <property> elements specify default values for element attributes, such as timeout or bargein. For example, to turn off bargein by default for all the prompts in a particular form:
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="no_bargein_form">
<property name="bargein" value="false"/>
<block>
<prompt>
This introductory prompt cannot be barged into.
</prompt>
<prompt>
And neither can this prompt.
</prompt>
<prompt bargein="true">
But this one <emphasis>can</emphasis> be barged into.
</prompt>
</block>
<field type="boolean">
<prompt>
Please say yes or no.
</prompt>
</field>
</form>
</vxml>
An interpreter context is free to provide platform-specific properties. For example, to set the "multiplication factor" for this platform in the scope of this document:
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form>
<property name="com.example.multiplication_factor" value="42"/>
<block>
<prompt> Welcome </prompt>
</block>
</form>
</vxml>
By definition, platform-specific properties introduce incompatibilities which reduce application portability. To minimize them, the following interpreter context guidelines are strongly recommended:
Platform-specific properties should use reverse domain names to eliminate potential collisions as in: com.example.foo, which is clearly different from net.example.foo
An interpreter context must not throw an error.unsupported.property event when encountering a property it cannot process; rather the interpreter context must just ignore that property.
The generic speech recognizer properties mostly are taken from the Java Speech API [JSAPI]:
| confidencelevel | The speech recognition confidence level, a float value in the range of 0.0 to 1.0. Results are rejected (a nomatch event is thrown) when application.lastresult$.confidence is below this threshold. A value of 0.0 means minimum confidence is needed for a recognition, and a value of 1.0 requires maximum confidence. The value is a Real Number Designation (see Section 6.5). The default value is 0.5. |
|---|---|
| sensitivity | Set the sensitivity level. A value of 1.0 means that it is highly sensitive to quiet input. A value of 0.0 means it is least sensitive to noise. The value is a Real Number Designation (see Section 6.5). The default value is 0.5. |
| speedvsaccuracy | A hint specifying the desired balance between speed vs. accuracy. A value of 0.0 means fastest recognition. A value of 1.0 means best accuracy. The value is a Real Number Designation (see Section 6.5). The default is value 0.5. |
| completetimeout |
The length of silence required following user speech before the speech recognizer finalizes a result (either accepting it or throwing a nomatch event). The complete timeout is used when the speech is a complete match of an active grammar. By contrast, the incomplete timeout is used when the speech is an incomplete match to an active grammar. A long complete timeout value delays the result completion and therefore makes the computer's response slow. A short complete timeout may lead to an utterance being broken up inappropriately. Reasonable complete timeout values are typically in the range of 0.3 seconds to 1.0 seconds. The value is a Time Designation (see Section 6.5). The default is platform-dependent. See Appendix D. Although platforms must parse the completetimeout property, platforms are not required to support the behavior of completetimeout. Platforms choosing not to support the behavior of completetimeout must so document and adjust the behavior of the incompletetimeout property as described below. |
| incompletetimeout |
The required length of silence following user speech after which a recognizer finalizes a result. The incomplete timeout applies when the speech prior to the silence is an incomplete match of all active grammars. In this case, once the timeout is triggered, the partial result is rejected (with a nomatch event). The incomplete timeout also applies when the speech prior to the silence is a complete match of an active grammar, but where it is possible to speak further and still match the grammar. By contrast, the complete timeout is used when the speech is a complete match to an active grammar and no further words can be spoken. A long incomplete timeout value delays the result completion and therefore makes the computer's response slow. A short incomplete timeout may lead to an utterance being broken up inappropriately. The incomplete timeout is usually longer than the complete timeout to allow users to pause mid-utterance (for example, to breathe). See Appendix D. Platforms choosing not to support the completetimeout property (described above) must use the maximum of the completetimeout and incompletetimeout values as the value for the incompletetimeout. The value is a Time Designation (see Section 6.5). |
| maxspeechtimeout |
The maximum duration of user speech. If this time elapsed before the user stops speaking, the event "maxspeechtimeout" is thrown. The value is a Time Designation (see Section 6.5). The default duration is platform-dependent. |
Several generic properties pertain to DTMF grammar recognition:
| interdigittimeout | The inter-digit timeout value to use when recognizing DTMF input. The value is a Time Designation (see Section 6.5). The default is platform-dependent. See Appendix D. |
|---|---|
| termtimeout | The terminating timeout to use when recognizing DTMF input. The value is a Time Designation (see Section 6.5). The default value is "0s". Appendix D. |
| termchar | The terminating DTMF character for DTMF input recognition. The default value is "#". See Appendix D. |
These properties apply to the fundamental platform prompt and collect cycle:
| bargein | The bargein attribute to use for prompts. Setting this to true allows bargein by default. Setting it to false disallows bargein. The default value is "true". |
|---|---|
| bargeintype | Sets the type of bargein to be speech or hotword. Default is platform-specific. See Section 4.1.5.1. |
| timeout | The time after which a noinput event is thrown by the platform. The value is a Time Designation (see Section 6.5). The default value is platform-dependent. See Appendix D. |
These properties pertain to the fetching of new documents and resources:
| audiofetchhint | This tells the platform whether or not it can attempt to optimize dialog interpretation by pre-fetching audio. The value is either safe to say that audio is only fetched when it is needed, never before; or prefetch to permit, but not require the platform to pre-fetch the audio. The default value is prefetch. |
|---|---|
| audiomaxage | Tells the platform the maximum acceptable age, in seconds, of cached audio resources. The default is platform-specific. |
| audiomaxstale | Tells the platform the maximum acceptable staleness, in seconds, of expired cached audio resources. The default is platform-specific. |
| documentfetchhint | Tells the platform whether or not documents may be pre-fetched. The value is either safe (the default), or prefetch. |
| documentmaxage | Tells the platform the maximum acceptable age, in seconds, of cached documents. The default is platform-specific. |
| documentmaxstale | Tells the platform the maximum acceptable staleness, in seconds, of expired cached documents. The default is platform-specific. |
| grammarfetchhint | Tells the platform whether or not grammars may be pre-fetched. The value is either prefetch (the default), or safe. |
| grammarmaxage | Tells the platform the maximum acceptable age, in seconds, of cached grammars. The default is platform-specific. |
| grammarmaxstale | Tells the platform the maximum acceptable staleness, in seconds, of expired cached grammars. The default is platform-specific. |
| objectfetchhint | Tells the platform whether the URI contents for <object> may be pre-fetched or not. The values are prefetch (the default), or safe. |
| objectmaxage | Tells the platform the maximum acceptable age, in seconds, of cached objects. The default is platform-specific. |
| objectmaxstale | Tells the platform the maximum acceptable staleness, in seconds, of expired cached objects. The default is platform-specific. |
| scriptfetchhint | Tells whether scripts may be pre-fetched or not. The values are prefetch (the default), or safe. |
| scriptmaxage | Tells the platform the maximum acceptable age, in seconds, of cached scripts. The default is platform-specific. |
| scriptmaxstale | Tells the platform the maximum acceptable staleness, in seconds, of expired cached scripts. The default is platform-specific. |
| fetchaudio | The URI of the audio to play while waiting for a document to be fetched. The default is not to play any audio during fetch delays. There are no fetchaudio properties for audio, grammars, objects, and scripts. The fetching of the audio clip is governed by the audiofetchhint, audiomaxage, audiomaxstale, and fetchtimeout properties in effect at the time of the fetch. The playing of the audio clip is governed by the fetchaudiodelay, and fetchaudiominimum properties in effect at the time of the fetch. |
|
fetchaudiodelay |
The time interval to wait at the start of a fetch delay before playing the fetchaudio source. The value is a Time Designation (see Section 6.5). The default interval is platform-dependent, e.g. "2s". The idea is that when a fetch delay is short, it may be better to have a few seconds of silence instead of a bit of fetchaudio that is immediately cut off. |
|
fetchaudiominimum |
The minimum time interval to play a fetchaudio source, once started, even if the fetch result arrives in the meantime. The value is a Time Designation (see Section 6.5). The default is platform-dependent, e.g., "5s". The idea is that once the user does begin to hear fetchaudio, it should not be stopped too quickly. |
| fetchtimeout | The timeout for fetches. The value is a Time Designation (see Section 6.5). The default value is platform-dependent. |
| inputmodes | This property determines which input modality to use. The input modes to enable: dtmf and voice. On platforms that support both modes, inputmodes defaults to "dtmf voice". To disable speech recognition, set inputmodes to "dtmf". To disable DTMF, set it to "voice". One use for this would be to turn off speech recognition in noisy environments. Another would be to conserve speech recognition resources by turning them off where the input is always expected to be DTMF. This property does not control the activation of grammars. For instance, voice-only grammars may be active when the inputmode is restricted to DTMF. Those grammars would not be matched, however, because the voice input modality is not active. |
|---|---|
|
universals |
Platforms may optionally provide platform-specific universal command grammars, such as "help", "cancel", or "exit" grammars, that are always active and which generate specific events. Production-grade applications often need to define their own universal command grammars, e.g., to increase application portability or to provide a distinctive interface. They specify new universal command grammars with <link> elements. They turn off the default grammars with this property. Default catch handlers are not affected by this property. The value "none" is the default, and means that all platform default universal command grammars are disabled. The value "all" turns them all on. Individual grammars are enabled by listing their names separated by spaces; for example, "cancel exit help". |
|
maxnbest |
This property controls the maximum size of the "application.lastresult$" array; the array is constrained to be no larger than the value specified by 'maxnbest'. This property has a minimum value of 1. The default value is 1. |
Our last example shows several of these properties used at multiple levels.
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<!-- set default characteristics for page -->
<property name="audiofetchhint" value="safe"/>
<property name="confidencelevel" value="0.75"/>
<form>
<!-- override defaults for this form only -->
<property name="confidencelevel" value="0.5"/>
<property name="bargein" value="false"/>
<grammar src="address_book.grxml" type="application/srgs+xml"/>
<block>
<prompt> Welcome to the Voice Address Book </prompt>
</block>
<initial name="start">
<!-- override default timeout value -->
<property name="timeout" value="5s"/>
<prompt> Who would you like to call? </prompt>
</initial>
<field name="person">
<prompt>
Say the name of the person you would like to call.
</prompt>
</field>
<field name="location">
<prompt>
Say the location of the person you would like to call.
</prompt>
</field>
<field name="confirm">
<grammar type="application/srgs+xml" src="/grammars/boolean.grxml"/>
<!-- Use actual utterances to playback recognized words,
rather than returned slot values -->
<prompt>
You said to call <value expr="person$.utterance"/>
at <value expr="location$.utterance"/>.
Is this correct?
</prompt>
<filled>
<if cond="confirm">
<submit namelist="person location"
next="http://www.messagecentral.example.com/voice/make_call" />
</if>
<clear/>
</filled>
</field>
</form>
</vxml>
The <param> element is used to specify values that are passed to subdialogs or objects. It is modeled on the [HTML] <PARAM> element. Its attributes are:
| name | The name to be associated with this parameter when the object or subdialog is invoked. |
|---|---|
| expr | An expression that computes the value associated with name. |
| value | Associates a literal string value with name. |
| valuetype | One of data or ref, by default data; used to indicate to an object if the value associated with name is data or a URI (ref). This is not used for <subdialog> since values are always data. |
| type | The media type of the result provided by a URI if the valuetype is ref; only relevant for uses of <param> in <object>. |
Exactly one of "expr" or "value" must be specified; otherwise, an error.badfetch event is thrown.
The use of valuetype and type is optional in general, although they may be required by specific objects. When <param> is contained in a <subdialog> element, the values specified by it are used to initialize dialog <var> elements in the subdialog that is invoked. When <param> is contained in an <object>, the use of the parameter data is specific to the object that is being invoked, and is outside the scope of the VoiceXML specification.
Below is an example of <param> used as part of an <object>. In this case, the first two <param> elements have expressions (implicitly of valuetype="data"), the third <param> has an explicit value, and the fourth is a URI that returns a media type of text/plain. The meaning of this data is specific to the object.
<object name="debit" classid="method://credit_card/gather_and_debit" data="http://www.recordings.example.com/prompts/credit/jesse.jar"> <param name="amount" expr="document.amt"/> <param name="vendor" expr="vendor_num"/> <param name="application_id" value="ADC5678-QWOO"/> <param name="authentication_server" value="http://auth_svr.example.com" valuetype="ref" type="text/plain"/> </object>
The next example illustrates <param> used with <subdialog>. In this case, two expressions are used to initialize variables in the scope of the subdialog form.
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form>
<subdialog name="result" src="http://another.example.com/#getssn">
<param name="firstname" expr="document.first"/>
<param name="lastname" expr="document.last"/>
<filled>
<submit namelist="result.ssn"
next="http://myservice.example.com/cgi-bin/process"/>
</filled>
</subdialog>
</form>
</vxml>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd">
<form id="getssn">
<var name="firstname"/>
<var name="lastname"/>
<field name="ssn">
<grammar src="http://grammarlib/ssn.grxml"
type="application/srgs+xml"/>
<prompt>
Please say social security number.
</prompt>
<filled>
<if cond="validssn(firstname,lastname,ssn)">
<assign name="status" expr="true"/>
<return namelist="status ssn"/>
<else/>
<assign name="status" expr="false"/>
<return namelist="status"/>
</if>
</filled>
</field>
</form>
</vxml>
Using <param> in a <subdialog> is a convenient way of passing data to a subdialog without requiring the use of server side scripting.
Several VoiceXML parameter values follow the conventions used in the W3C's Cascading Style Sheet recommendation [CSS2].
Real numbers and integers are specified in decimal notation only. An integer consists of one or more digits "0" to "9". A real number may be an integer, or it may be zero or more digits followed by a dot (.) followed by one or more digits. Both integers and real numbers may be preceded by a "-" or "+" to indicate the sign.
Time designations consist of a non-negative real number followed by a time unit identifier. The time unit identifiers are:
ms: milliseconds
s: seconds
Examples include: "3s", "850ms", "0.7s", ".5s" and "+1.5s".
The VoiceXML DTD is located at http://www.w3.org/TR/2003/CR-voicexml20-20030128/vxml.dtd.
Due to DTD limitations, the VoiceXML DTD does not correctly express that the <metadata> element can contain elements from other XML namespaces.
Note: the VoiceXML DTD includes modified elements from the DTDs of the Speech Recognition Grammar Specification 1.0 [SRGS] and the Speech Synthesis Markup Language 1.0 [SSML].
The form interpretation algorithm (FIA) drives the interaction between the user and a VoiceXML form or menu. A menu can be viewed as a form containing a single field whose grammar and whose <filled> action are constructed from the <choice> elements.
The FIA must handle:
Form initialization.
Prompting, including the management of the prompt counters needed for prompt tapering.
Grammar activation and deactivation at the form and form item levels.
Entering the form with an utterance that matched one of the form’s document-scoped grammars while the user was visiting a different form or menu.
Leaving the form because the user matched another form, menu, or link’s document-scoped grammar.
Processing multiple field fills from one utterance, including the execution of the relevant <filled> actions.
Selecting the next form item to visit, and then processing that form item.
Choosing the correct catch element to handle any events thrown while processing a form item.
First we define some terms and data structures used in the form interpretation algorithm:
Here is the conceptual form interpretation algorithm. The FIA can start with no initial utterance, or with an initial utterance passed in from another dialog:
// // Initialization Phase // foreach ( <var>, <script> and form item, in document order ) if ( the element is a <var> ) Declare the variable, initializing it to the value of the "expr" attribute, if any, or else to undefined. else if ( the element is a <script> ) Evaluate the contents of the script if inlined or else from the location specified by the "src" attribute. else if ( the element is a form item ) Create a variable from the "name" attribute, if any, or else generate an internal name. Assign to this variable the value of the "expr" attribute, if any, or else undefined. foreach ( input item and <initial> element ) Declare a prompt counter and set it to 1. if ( user entered this form by speaking to its grammar while in a different form) { Enter the main loop below, but start in the process phase, not the select phase: we already have a collection to process. } // // Main Loop: select next form item and execute it. // while ( true ) { // // Select Phase: choose a form item to visit. // if ( the last main loop iteration ended with a <goto nextitem> ) Select that next form item. else if (there is a form item with an unsatisfied guard condition ) Select the first such form item in document order. else Do an <exit/> -- the form is full and specified no transition. // // Collect Phase: execute the selected form item. // // Queue up prompts for the form item. unless ( the last loop iteration ended with a catch that had no <reprompt>, and the active dialog was not changed ) { Select the appropriate prompts for an input item or <initial>. Queue the selected prompts for play prior to the next collect operation. Increment an input item’s or <initial>'s prompt counter. } // Activate grammars for the form item. if ( the form item is modal ) Set the active grammar set to the form item grammars, if any. (Note that some form items, e.g. <block>, cannot have any grammars). else Set the active grammar set to the form item grammars and any grammars scoped to the form, the current document, and the application root document. // Execute the form item. if ( a <field> was selected ) Collect an utterance or an event from the user. else if ( a <record> was chosen ) Collect an utterance (with a name/value pair for the recorded bytes) or event from the user. else if ( an <object> was chosen ) Execute the object, setting the <object>’s form item variable to the returned ECMAScript value. else if ( a <subdialog> was chosen ) Execute the subdialog, setting the <subdialog>’s form item variable to the returned ECMAScript value. else if ( a <transfer> was chosen ) Do the transfer, and (if wait is true) set the <transfer> form item variable to the returned result status indicator. else if ( an <initial> was chosen ) Collect an utterance or an event from the user. else if ( a <block> was chosen ) { Set the block’s form item variable to a defined value. Execute the block’s executable context. } // // Process Phase: process the resulting utterance or event. // Assign the utterance and other information about the last recognition to application.lastresult$. // Must have an utterance if ( the utterance matched a grammar belonging to a <link> ) If the link specifies an "next" or "expr" attribute, transition to that location. Else if the link specifies an "event" or "eventexpr" attribute, generate that event. else if ( the utterance matched a grammar belonging to a <choice> ) If the choice specifies an "next" or "expr" attribute, transition to that location. Else if the choice specifies an "event" or "eventexpr" attribute, generate that event. else if ( the utterance matched a grammar from outside the current <form> or <menu> ) { Transition to that <form> or <menu>, carrying the utterance to the new FIA. } // Process an utterance spoken to a grammar from this form. // First copy utterance result property values into corresponding // form item variables. Clear all "just_filled" flags. if ( the grammar is scoped to the field-level ) { // This grammar must be enclosed in an input item. The input item // has an associated ECMAScript variable (referred to here as the input // item variable) and slot name. if ( the result is not a structure ) Copy the result into the input item variable. elseif ( a top-level property in the result matches the slot name or the slot name is a dot-separated path matching a subproperty in the result ) Copy the value of that property into the input item variable. else Copy the entire result into the input item variable Set this input item's "just_filled" flag. } else { foreach ( property in the user’s utterance ) { if ( the property matches an input item’s slot name ) { Copy the value of that property into the input item’s form item variable. Set the input item’s "just_filled" flag. } } } // Set all <initial> form item variables if any input items are filled. if ( any input item variable is set as a result of the user utterance ) Set all <initial> form item variables to true. // Next execute any <filled> actions triggered by this utterance. foreach ( <filled> action in document order ) { // Determine the input item variables the <filled> applies to. N = the <filled>’s "namelist" attribute. if ( N equals "" ) { if ( the <filled> is a child of an input item ) N = the input item’s form item variable name. else if ( the <filled> is a child of a form ) N = the form item variable names of all the input items in that form. } // Is the <filled> triggered? if ( any input item variable in the set N was "just_filled" AND ( the <filled> mode is "all" AND all variables in N are filled OR the <filled> mode is "any" AND any variables in N are filled) ) Execute the <filled> action. If an event is thrown during the execution of a <filled>, event handler selection starts in the scope of the <filled>, which could be an input item or the form itself. } // If no input item is filled, just continue. }
During FIA execution, events may be generated at several points. These events are processed differently depending on which phase is active.
Before a form item is selected (i.e. during the Initialization and Select phases), events are generated at the dialog level. The corresponding catch handler is located and executed. If the catch does not result in a transition from the current dialog, FIA execution will terminate.
Similarly, events triggered after a form item is selected (i.e. during the Collect and Process phases) are usually generated at the form item level. There is one exception: events triggered by a dialog level <filled> are generated at the dialog level. The corresponding catch handler is located and executed. If the catch does not result in a transition, the current FIA loop is terminated and Select phase is reentered.
The various timing properties for speech and DTMF recognition work together to define the user experience. The ways in which these different timing parameters function are outlined in the timing diagrams below. In these diagrams, the start for wait of DTMF input, or user speech both occur at the time that the last prompt has finished playing.
DTMF grammars use timeout, interdigittimeout, termtimeout and termchar as described in Section 6.3.3 to tailor the user experience. The effects of these are shown in the following timing diagrams.
The timeout parameter determines when the <noinput> event is thrown because the user has failed to enter any DTMF (Figure 12). Once the first DTMF has been entered, this parameter has no further effect.
Figure 12: Timing
diagram for timeout when no input provided.
In Figure 13, the interdigittimeout determines when the nomatch event is thrown because a DTMF grammar is not yet recognized, and the user has failed to enter additional DTMF.
Figure 13: Timing
diagram for interdigittimeout, grammar is not ready to terminate.
The example below shows the situation when a DTMF grammar could terminate, or extend by the addition of more DTMF input, and the user has elected not to provide any further input.
Figure 14: Timing
diagram for interdigittimeout, grammar is ready to terminate.
In the example below, a termchar is non-empty, and is entered by the user before an interdigittimeout expires, to signify that the users DTMF input is complete; the termchar is not included as part of the recognized value.
Figure 15: Timing
diagram for termchar and interdigittimeout, grammar can terminate.
In the example below, the entry of the last DTMF has brought the grammar to a termination point at which no additional DTMF is expected. Since termchar is empty, there is no optional terminating character permitted, thus the recognition ends and the recognized value is returned.
Figure 16: Timing
diagram for termchar empty when grammar must terminate.
In the example below, the entry of the last DTMF has brought the grammar to a termination point at which no additional DTMF is allowed by the grammar. If the termchar is non-empty, then the user can enter an optional termchar DTMF. If the user fails to enter this optional DTMF within termtimeout, the recognition ends and the recognized value is returned. If the termtimeout is 0s (the default), then the recognized value is returned immediately after the last DTMF allowed by the grammar, without waiting for the optional termchar. Note: the termtimeout applies only when no additional input is allowed by the grammar; otherwise, the interdigittimeout applies.
Figure 17: Timing
diagram for termchar non-empty and termtimeout when grammar must terminate.
In this example, the entry of the last DTMF has brought the grammar to a termination point at which no additional DTMF is allowed by the grammar. Since the termchar is non-empty, the user enters the optional termchar within termtimeout causing the recognized value to be returned (excluding the termchar).
Figure 18: Timing
diagram for termchar non-empty when grammar must terminate.
While waiting for the first or additional DTMF, three different timeouts may determine when the user's input is considered complete. If no DTMF has been entered, the timeout applies; if some DTMF has been entered but additional DTMF is valid, then the interdigittimeout applies; and if no additional DTMF is legal, then the termtimeout applies. At each point, the user may enter DTMF which is not permitted by the active grammar(s). This causes the collected DTMF string to be invalid. Additional digits will be collected until either the termchar is pressed or the interdigittimeout has elapsed. A nomatch event is then generated.
Speech grammars use timeout, completetimeout, and incompletetimeout as described in Section 6.3.4 and Section 6.3.2 to tailor the user experience. The effects of these are shown in the following timing diagrams.
In the example below, the timeout parameter determines when the noinput event is thrown because the user has failed to speak.
Figure 19: Timing
diagram for timeout when no speech provided.
In the example above, the user provided a utterance that was recognized by the speech grammar. After a silence period of completetimeout has elapsed, the recognized value is returned.
Figure 20: Timing
diagram for completetimeout with speech grammar recognized.
In the example above, the user provided a utterance that is not as yet recognized by the speech grammar but is the prefix of a legal utterance. After a silence period of incompletetimeout has elapsed, a nomatch event is thrown.
Figure 21: Timing
diagram for incompletetimeout with speech grammar unrecognized.
VoiceXML requires that a platform support the playing and recording audio formats specified below.
| Audio Format | Media Type |
|---|---|
| Raw (headerless) 8kHz 8-bit mono mu-law [PCM] single channel. (G.711) | audio/basic (from [RFC1521]) |
| Raw (headerless) 8kHz 8 bit mono A-law [PCM] single channel. (G.711) | audio/x-alaw-basic |
| WAV (RIFF header) 8kHz 8-bit mono mu-law [PCM] single channel. | audio/x-wav |
| WAV (RIFF header) 8kHz 8-bit mono A-law [PCM] single channel. | audio/x-wav |
The 'audio/basic' mime type is commonly used with the 'au' header format as well as the headerless 8-bit 8Khz mu-law format. If this mime type is specified for recording, the mu-law format must be used. For playback with the 'audio/basic' mime type, platforms must support the mu-law format and may support the 'au' format.
This section is Normative.
A conforming VoiceXML document is a well-formed [XML] document that requires only the facilities described as mandatory in this specification. Such a document must meet all of the following criteria:
The document must conform to the constraints expressed in the VoiceXML Schema (Appendix O).
The root element of the document must be <vxml>.
The <vxml> element must include a "version" attribute with the value "2.0".
The <vxml> element must designate the VoiceXML namespace using the "xmlns" attribute [XMLNAMES]. The namespace for VoiceXML is defined to be http://www.w3.org/2001/vxml.
It is recommended that the <vxml> element also include "xmlns:xsi" and "xsi:schemaLocation" attributes to indicate the location of the schema for the VoiceXML namespace. If the "xsi:schemaLocation" attribute is present, it must include a reference to the VoiceXML Schema:
xsi:schemaLocation="http://www.w3.org/2001/vxml http://www.w3.org/TR/voicexml20/vxml.xsd"
There may be a DOCTYPE declaration in the document prior to the root element. If present, the public identifier included in the DOCTYPE declaration must reference the VoiceXML DTD (Appendix B) using its Formal Public Identifier.
<!DOCTYPE vxml
PUBLIC "-//W3C//DTD VOICEXML 2.0//EN"
"http://www.w3.org/TR/voicexml20/vxml.dtd">
The system identifier may be modified appropriately.
The DTD subset must not be used to override any parameter entities in the DTD.
Here is an example of a Conforming VoiceXML document:
<?xml version="1.0" encoding="UTF-8"?> <vxml version="2.0" xmlns="http://www.w3.org/2001/vxml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.w3.org/2001/vxml http://www.w3.org/TR/voicexml20/vxml.xsd"> <form> <block>hello</block> </form> </vxml>
Note that in this example, the recommended "xmlns:xsi" and "xsi:schemaLocation" attributes are included as is an XML declaration. An XML declaration like the one above is not required in all XML documents. VoiceXML document authors are strongly encouraged to use XML declarations in all their documents. Such a declaration is required when the character encoding of the document is other than the default UTF-8 or UTF-16 and no encoding was determined by a higher-level protocol.
The VoiceXML language or these conformance criteria provide no designated size limits on any aspect of VoiceXML documents. There are no maximum values on the number of elements, the amount of character data, or the number of characters in attribute values.
The VoiceXML namespace may be used with other XML namespaces as per [XMLNAMES], although such documents are not strictly conforming VoiceXML documents as defined above. Future work by W3C will address ways to specify conformance for documents involving multiple namespaces.
A VoiceXML processor is a user agent that can parse and process Conforming VoiceXML documents.
In a Conforming VoiceXML Processor, the XML parser must be able to parse and process all well-formed XML constructs defined within [XML] and [XMLNAMES]. It is not required that a Conforming VoiceXML processor use a validating parser.
A Conforming VoiceXML Processor must be a Conforming Speech Synthesis Markup Language Processor [SSML] and a Conforming XML Grammar Processor [SRGS] except for differences described in this document. If a syntax error is detected processing a grammar document, then an "error.badfetch" event must be thrown.
A Conforming VoiceXML Processor must support the syntax and semantics of all VoiceXML elements as described in this document. Consequently, a Conforming VoiceXML Processor must not throw an 'error.unsupported.<element>' for any VoiceXML element which must be supported when processing a Conforming VoiceXML Document.
When a Conforming VoiceXML Processor encounters a Conforming VoiceXML Document with non-VoiceXML elements or attributes which are proprietary, defined only in earlier versions of VoiceXML, or defined in a non-VoiceXML namespace, and which cannot be processed, then it must throw an "error.badfetch" event.
When a Conforming VoiceXML Processor encounters a document with a root element designating a namespace other than VoiceXML, its behavior is undefined.
There is, however, no conformance requirement with respect to performance characteristics of the VoiceXML Processor.
VoiceXML is an application of [XML] and thus supports [UNICODE] which defines a standard universal character set.
Additionally, VoiceXML provides a mechanism for precise control of the input and output languages via the use of "xml:lang" attribute. This facility provides:
Voice is central to, but not the limit of, VoiceXML applications. While speaking and listening will be the most widely used techniques in most circumstances and for most users to interact with VoiceXML applications, some users may be unable to speak and/or listen because of temporary (or permanent) circumstances. Persons with disabilities, particularly those with speech and/or hearing impairments, may need to interact with VoiceXML applications in other ways:
<audio src="greetings.wav">Greetings</audio>would normally replay the greetings.wav audio file. However, if the VoiceXML Interpreter Context has detected that the user is viewing the interaction on a display or is touching Braille output, then the text "Greetings" is rendered by the display or Braille output device.
Providing alternative paths to information delivery and user input is central to all W3C technologies intended for use by people. While initially authored to make on screen content accessible, the following accessibility guidelines published by W3C's Web Accessibility Initiative (WAI) also apply to VoiceXML.
Additional guidelines for enabling persons with disabilities to access VoiceXML applications include the following:
A future version of VoiceXML may specify criteria by which a VoiceXML Processor safeguards the privacy of personal data.
The following is a summary of the differences between VoiceXML 2.0 and VoiceXML 1.0 [VOICEXML-1.0].
Developers of VoiceXML 1.0 applications should pay particular attentions to the changes incompatible with VoiceXML 1.0 specified in Obsolete Elements and Incompatibly Modified Elements.
Definition: A packaged application fragment designed to be invoked by arbitrary applications or other Reusable Dialog Components. A Reusable Dialog Component (RDC) encapsulates the code for an interaction with the caller.
Reusable dialog components provide pre-packaged functionality "out-of-the-box" that enables developers to quickly build applications by providing standard default settings and behavior. They shield developers from having to worry about many of the intricacies associated with building a robust speech dialog, e.g., confidence score interpretation, error recovery mechanisms, prompting, etc. This behavior can be customized by a developer if necessary to provide application-specific prompts, vocabulary, retry settings, etc.
In this version of VoiceXML, the only authentic reusable component calling mechanisms are <subdialog> and <object>. Components called this way follow a model similar to subroutines in programming languages: the component is configured by a well-defined set of parameters passed to the component, the component has a relatively constrained interaction with the calling application, the component returns a well-defined result, and control returns automatically to the point from which the component was called. This has all the significant advantages of modularity, reentrancy, and easy reuse provided by subroutines. Of the two kinds of components, only <subdialog> components are guaranteed to be as portable as VoiceXML itself. On the other hand, <object> components may be able to package advanced, reusable functionality that has not yet been introduced into the standard.
Although reusable dialog components have the advantages of modularity, reentrancy, and easy reuse as described above, the disadvantage of such components is that they must be designed very carefully with an eye to reuse, and even with the most careful of designs it is possible that the application developer will encounter situations for which the component cannot be easily configured to handle the application requirements. In addition, while the constrained interaction of a component with its calling environment makes it possible for the component designer to create a component that works predictably in disparate environments, it also may make the user's interaction with the component seem disconnected from the rest of the application.
In such situations the application developer may wish to reuse VoiceXML source code in the form of samples and templates - samples designed for easy customizability. Such code is more easily tailored for and integrated into a particular application, at the expense of modularity and rentrancy.
Such templates and samples can be created by separating interesting VoiceXML code from a main dialog and then distributing that code by copy for use in other dialogs. This form of reusability allows the user of the copied VoiceXML code to modify it as necessary and continue to use their modified version indefinitely.
VoiceXML facilitates this form of reusability by preserving the separation of state between form elements. In this regard, VoiceXML and [HTML] are similar. An HTML table can be copied from one HTML page to another because the table can be displayed regardless of the context before or after the table element.
Although parameterizability, modularity, and maintainability may be sacrificed with this approach, it has the advantage of being simple, quick, and eminently customizable.
This W3C specification is based upon VoiceXML 1.0 submitted by the VoiceXML Forum in May 2000. The VoiceXML Forum authors were: Linda Boyer, IBM; Peter Danielsen, Lucent Technologies; Jim Ferrans, Motorola; Gerald Karam, AT&T; David Ladd, Motorola; Bruce Lucas, IBM; Kenneth Rehor, Lucent Technologies.
This version was written with the participation of members of the W3C Voice Browser Working Group. The following have significantly contributed to writing this specification:
The Working Group would like to thank Dave Raggett and Jim Larson for their invaluable management support.
The W3C Voice Browser Working Group has applied to IETF to register a media type for VoiceXML (http://www.ietf.org/internet-drafts/draft-tryphonas-voicexml-media-reg-01.txt). The requested media type is application/voicexml+xml.
The W3C Voice Browser Working Group has adopted the convention of using the ".vxml" filename suffix for VoiceXML documents.
This section is Normative.
The VoiceXML schema is located at http://www.w3.org/TR/2003/CR-voicexml20-20030128/vxml.xsd.
The VoiceXML schema depends upon other schema defined in the VoiceXML namespace:
The complete set of Speech Interface Framework schema required for VoiceXML 2.0 is available here.
The <field> type attribute in Section 2.3.1 is used to specify a builtin grammar for one of the fundamental types. Platform support for fundamental builtin grammars is optional. If a platform does support builtin types, then it must follow the description given in this appendix as closely as possible, including all the builtins for a given language.
Each builtin type has a convention for the format of the value returned. These are independent of language and of the implementation. The return type for builtin fields is a string except for the boolean field type. To access the actual recognition result, the author can reference the <field> shadow variable name$.utterance. Alternatively, the developer can access application.lastresult$, where application.lastresult$.interpretation has the same string value as application.lastresult$.utterance.
The builtin types are defined in such a way that a VoiceXML application developer can assume some consistency of user input across implementations. This permits help messages and other prompts to be independent of platform in many instances. For example, the boolean type’s grammar should minimally allow "yes" and "no" responses in English, but each implementation is free to add other choices, such as "yeah" and "nope".
In cases where an application requires specific behavior or different behavior than defined for a builtin, it should use an explicit field grammar. The following are circumstances in which an application must provide an explicit field grammar in order to ensure portability of the application with a consistent user interface:
A platform is not required to implement a grammar that accepts all possible values that might be returned by a builtin. For instance, the currency builtin defines the return value formatting for a very broad range of currencies ([ISO4217]). The platform is not required to support spoken input that includes any of the world's currencies since that can negatively impact recognition accuracy. Similarly, the number builtin can return positive or negative floating point numbers but the grammar is not required to support all possible spoken floating point numbers.
Builtins are also limited in their ability to handle underspecified spoken input. For instance, "20 peso" cannot be resolved to a specific [ISO4217] currency code because the "peso" is the name of the currency of numerous nations. In such cases the platform may return a specific currency code according to the language or may omit the currency code.
All builtin types must support both voice and DTMF entry.
The set of accepted spoken input for each builtin type is platform dependent and will vary by language.
The value returned by a builtin type can be read out using the <say-as> element. VoiceXML extends <say-as> in [SSML] by adding 'interpret-as' values corresponding to each builtin type. These values take the form "vxml:<type>" where type is a builtin type. The precise rendering of builtin types is platform-specific and will vary by language.
The builtin types are:
| boolean | Inputs include affirmative and negative phrases appropriate to the current language. DTMF 1 is affirmative and 2 is negative. The result is ECMAScript true for affirmative or false for negative. The value will be submitted as the string "true" or the string "false". If the field value is subsequently used in <say-as> with the interpret-as value "vxml:boolean", it will be spoken as an affirmative or negative phrase appropriate to the current language. |
|---|---|
| date | Valid spoken inputs include phrases that specify a date, including a month day and year. DTMF inputs are: four digits for the year, followed by two digits for the month, and two digits for the day. The result is a fixed-length date string with format yyyymmdd, e.g. "20000704". If the year is not specified, yyyy is returned as "????"; if the month is not specified mm is returned as "??"; and if the day is not specified dd is returned as "??". If the value is subsequently used in <say-as> with the interpret-as value "vxml:date", it will be spoken as date phrase appropriate to the current language. |
| digits | Valid spoken or DTMF inputs include one or more digits, 0 through 9. The result is a string of digits. If the result is subsequently used in <say-as> with the interpret-as value "vxml:digits", it will be spoken as a sequence of digits appropriate to the current language. A user can say for example "two one two seven", but not "twenty one hundred and twenty-seven". A platform may support constructs such as "two double-five eight". |
| currency | Valid spoken inputs include phrases that specify a currency amount. For DTMF input, the "*" key will act as the decimal point. The result is a string with the format UUUmm.nn, where UUU is the three character currency indicator according to ISO standard 4217 [ISO4217], or mm.nn if the currency is not spoken by the user or if the currency cannot be reliably determined (e.g. "dollar" and "peso" are ambiguous). If the field is subsequently used in <say-as> with the interpret-as value "vxml:currency", it will be spoken as a currency amount appropriate to the current language. |
| number | Valid spoken inputs include phrases that specify numbers, such as "one hundred twenty-three", or "five point three". Valid DTMF input includes positive numbers entered using digits and "*" to represent a decimal point. The result is a string of digits from 0 to 9 and may optionally include a decimal point (".") and/or a plus or minus sign. ECMAScript automatically converts result strings to numerical values when used in numerical expressions. The result must not use a leading zero (which would cause ECMAScript to interpret as an octal number). If the field is subsequently used in <say-as> with the interpret-as value "vxml:number", it will be spoken as a number appropriate to the current language. |
| phone | Valid spoken inputs include phrases that specify a phone number. DTMF asterisk "*" represents "x". The result is a string containing a telephone number consisting of a string of digits and optionally containing the character "x" to indicate a phone number with an extension. For North America, a result could be "8005551234x789". If the field is subsequently used in <say-as> with the interpret-as value "vxml:phone", it will be spoken as a phone number appropriate to the current language. |
| time | Valid spoken inputs include phrases that specify a time, including hours and minutes. The result is a five character string in the format hhmmx, where x is one of "a" for AM, "p" for PM, "h" to indicate a time specified using 24 hour clock, or "?" to indicate an ambiguous time. Input can be via DTMF. Because there is no DTMF convention for specifying AM/PM, in the case of DTMF input, the result will always end with "h" or "?". If the field is subsequently used in <say-as> with the interpret-as value "vxml:time", it will be spoken as a time appropriate to the current language. |
An example of a <field> element with a builtin grammar type:
<field name="lo_fat_meal" type="boolean">
<prompt>
Do you want a low fat meal on this flight?
</prompt>
<help>
Low fat means less than 10 grams of fat, and under
250 calories.
</help>
<filled>
<prompt>
I heard <emphasis><say-as interpret-as="vxml:boolean">
<value expr="lo_fat_meal"/></say-as></emphasis>.
</prompt>
</filled>
</field>
In this example, the boolean type indicates that inputs are various forms of true and false. The value actually put into the field is either true or false. The field would be read out using the appropriate affirmative or negative response in prompts.
In the next example, digits indicates that input will be spoken or keyed digits. The result is stored as a string, and rendered as digits using the <say-as> with "vxml:digits" as the value for the interpret-as attribute, i.e., "one-two-three", not "one hundred twenty-three". The <filled> action tests the field to see if it has 12 digits. If not, the user hears the error message.
<field name="ticket_num" type="digits">
<prompt>
Read the 12 digit number from your ticket.
</prompt>
<help>The 12 digit number is to the lower left.</help>
<filled>
<if cond="ticket_num.length != 12">
<prompt>
Sorry, I didn't hear exactly 12 digits.
</prompt>
<assign name="ticket_num" expr="undefined"/>
<else/>
<prompt>I heard <say-as interpret-as="vxml:digits">
<value expr="ticket_num"/></say-as>
</prompt>
</if>
</filled>
</field>
The builtin boolean grammar and builtin digits grammar can be parameterized. This is done by explicitly referring to builtin grammars using a platform-specific builtin URI scheme and using a URI-style query syntax of the form type?param=value in the src attribute of a <grammar> element, or in the type attribute of a field, for example:
<grammar src="builtin:dtmf/boolean?y=7;n=9"/>
<field type="boolean?y=7;n=9">
<prompt>
If this is correct say yes or press seven, if not, say no or press nine.
</prompt>
</field>
<field type="digits?minlength=3;maxlength=5">
<prompt>Please enter your passcode</prompt>
</field>
Where the <grammar> parameterizes the builtin DTMF grammar, the first <field> parameterizes the builtin DTMF grammar (the speech grammar will be activated as normal) and the second <field> parameterizes both builtin DTMF and speech grammars. Parameters which are undefined for a given grammar type will be ignored; for example, "builtin:grammar/boolean?y=7".
The digits and boolean grammars can be parameterized as follows:
| digits?minlength=n | A string of at least n digits. Applicable to speech and DTMF grammars. If minlength conflicts with either the length or maxlength attributes then a error.badfetch event is thrown. |
|---|---|
| digits?maxlength=n | A string of at most n digits. Applicable to speech and DTMF grammars. If maxlength conflicts with either the length or minlength attributes then a error.badfetch event is thrown. |
| digits?length=n | A string of exactly n digits. Applicable to speech and DTMF grammars. If length conflicts with either the minlength or maxlength attributes then a error.badfetch event is thrown. |
| boolean?y=d | A grammar that treats the keypress d as an affirmative answer. Applicable only to the DTMF grammar. |
| boolean?n=d | A grammar that treats the keypress d as a negative answer. Applicable only to the DTMF grammar. |
Note that more than one parameter may be specified separated by ";" as illustrated above. When a <grammar> element with the mode set to "voice" (the default value) is specified in a <field>, it is in addition to the default speech grammar implied by the type attribute of the field. Likewise, when a <grammar> element with the mode set to "dtmf" is specified in a <field>, it is in addition to the default DTMF grammar.