VoiceXML language

This section provides a brief introduction to basic VoiceXML concepts and constructs. It describes IBM's implementation of Version 2.1 of VoiceXML and provides an overview of the differences between VoiceXML Version 2.0 and Version 2.1. The information provided in this section is not a complete description of the functionality of the language. Refer to the VoiceXML 2.1 specification at http://www.w3.org/TR/voicexml21/ for more information.

This section discusses the following topics:

Changes from VoiceXML 2.0
This section describes the changes added to VoiceXML in the 2.1 specification, as compared to VoiceXML 2.0. For a complete description of the differences between VoiceXML version 2.0 and version 2.1, refer to http://www.w3.org/TR/voicexml21/ .
The structure of a VoiceXML application
A VoiceXML application is made up of one or more VoiceXML documents that together control the dialog with the caller. These documents typically consist of a single root document, and several leaf documents. Application specific information such as global commands, event handlers and global variables, are typically defined within the root document, while individual dialogs and local variables are placed in leaf documents. A leaf document indicates that it is part of a larger application by using the application attribute on the <vxml> element to specfy the URI of the application's root document.
A simple VoiceXML example
The following example illustrates the basic dialog capabilities of VoiceXML using a menu and a form:
VoiceXML elements and attributes
VoiceXML is an XML-based application, meaning that it is defined as a set of XML tags or elements. The VoiceXML elements and provides implementation details specific to the VoiceXML browser in the Blueworx Voice Response product are listed here.
Speech Synthesis Markup Language (SSML)
The Speech Synthesis Markup Language (SSML) is an XML based markup language for handling TTS within a VoiceXML application. VoiceXML 2.0 inherits a set of SSML 1.0 elements, as described in more detail in the VoiceXML 2.0 specification.
Built-in field types and grammars
The VoiceXML browser supports the complete set of built-in field types that are defined in VoiceXML 2.1. These built-in field types specify the built-in grammar to load (which determines valid spoken and DTMF input) and how the TTS engine will pronounce the value in a prompt, are documented here.
Recorded audio
VoiceXML supports the use of recorded audio files for output. The VoiceXML browser plays an audio file when the corresponding URI ( <audio src=“URI of the audio prompt”> ) is encountered in a VoiceXML document.
Document fetching and caching
The VoiceXML browser uses caching to improve performance when fetching documents and other resources (such as audio files, grammars, and scripts); see Fetching and caching resources for improved performance.
Events
The VoiceXML browser throws an event when it encounters a <throw> element or when certain specified conditions occur; these may be normal error conditions (such as a recognition error) or abnormal error conditions (such as an invalid page reference). Events are caught by <catch> elements that can be specified within other VoiceXML elements in which the event can occur, or inherited from higher-level elements.
Variables and expressions
You can specify an executable ECMAScript enclosed within a <script> element or in an external file identified by the src attribute.
Grammars
A grammar is an enumeration, in compact form, of the set of utterances—words and phrases—that constitute the acceptable user response to a given prompt. The VoiceXML Browser currently supports only Speech Recognition Grammar Specification (SRGS) XML format and ABNF form grammars.
Timeout properties
The information in this section is intended as a clarification of the information in the VoiceXML 2.1 specification.
Telephony functionality
The VoiceXML browser supports the following telephony features for use in a connection environment: