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VoiceXML (VXML) is a digital document standard for specifying interactive media and voice dialogs between humans and computers. It is used for developing audio and voice response applications, such as banking systems and automated customer service portals. VoiceXML applications are developed and deployed in a manner analogous to how aweb browser interprets and visually renders theHypertext Markup Language (HTML) it receives from aweb server. VoiceXML documents are interpreted by avoice browser and in common deployment architectures, users interact with voice browsers via thepublic switched telephone network (PSTN).
The VoiceXML document format is based onExtensible Markup Language (XML). It is a standard developed by theWorld Wide Web Consortium (W3C).
VoiceXML applications are commonly used in many industries and segments of commerce. These applications include order inquiry, package tracking, driving directions, emergency notification, wake-up, flight tracking, voice access to email, customer relationship management, prescription refilling, audio news magazines, voice dialing, real-estate information and nationaldirectory assistance applications.[citation needed]
VoiceXML has tags that instruct thevoice browser to providespeech synthesis, automaticspeech recognition, dialog management, and audio playback. The following is an example of a VoiceXML document:
<vxmlversion="2.0"xmlns="http://www.w3.org/2001/vxml"><form><block><prompt>Helloworld!</prompt></block></form></vxml>
When interpreted by a VoiceXML interpreter this will output "Hello world" with synthesized speech.
Typically,HTTP is used as the transport protocol for fetching VoiceXML pages. Some applications may use static VoiceXML pages, while others rely on dynamic VoiceXML page generation using anapplication server likeTomcat,Weblogic,IIS, orWebSphere.
Historically, VoiceXML platform vendors have implemented the standard in different ways, and added proprietary features. But the VoiceXML 2.0 standard, adopted as a W3C Recommendation on 16 March 2004, clarified most areas of difference. The VoiceXML Forum, an industry group promoting the use of the standard, provides aconformance testing process that certifies vendors' implementations as conformant.
AT&T Corporation,IBM,Lucent, andMotorola formed the VoiceXML Forum in March 1999, in order to develop a standard markup language for specifying voice dialogs. By September 1999 the Forum released VoiceXML 0.9 for member comment, and in March 2000 they published VoiceXML 1.0. Soon afterwards, the Forum turned over the control of the standard to the W3C.[1] The W3C produced several intermediate versions of VoiceXML 2.0, which reached the final "Recommendation" stage in March 2004.[2]
VoiceXML 2.1 added a relatively small set of additional features to VoiceXML 2.0, based on feedback from implementations of the 2.0 standard. It is backward compatible with VoiceXML 2.0 and reached W3C Recommendation status in June 2007.[3]
VoiceXML 3.0 was slated to be the next major release of VoiceXML, with new major features. However, with the disbanding of the VoiceXML Forum in May 2022,[4] the development of the new standard was scrapped.
As of December 2022, there are few VoiceXML 2.0/2.1 platform implementations being offered.
The W3C's Speech Interface Framework also defines these other standards closely associated with VoiceXML.
TheSpeech Recognition Grammar Specification (SRGS) is used to tell the speech recognizer what sentence patterns it should expect to hear: these patterns are called grammars. Once the speech recognizer determines the most likely sentence it heard, it needs to extract the semantic meaning from that sentence and return it to the VoiceXML interpreter. This semantic interpretation is specified via theSemantic Interpretation for Speech Recognition (SISR) standard. SISR is used inside SRGS to specify the semantic results associated with the grammars, i.e., the set of ECMAScript assignments that create the semantic structure returned by the speech recognizer.
TheSpeech Synthesis Markup Language (SSML) is used to decorate textual prompts with information on how best to render them in synthetic speech, for example which speech synthesizer voice to use or when to speak louder or softer.
ThePronunciation Lexicon Specification (PLS) is used to define how words are pronounced. The generated pronunciation information is meant to be used by both speech recognizers and speech synthesizers in voice browsing applications.
TheCall Control eXtensible Markup Language (CCXML) is a complementary W3C standard. A CCXML interpreter is used on some VoiceXML platforms to handle the initial call setup between the caller and the voice browser, and to provide telephony services like call transfer and disconnect to the voice browser. CCXML can also be used in non-VoiceXML contexts.
Inmedia server applications, it is often necessary for several call legs to interact with each other, for example in a multi-party conference. Some deficiencies were identified in VoiceXML for this application and so companies designed specific scripting languages to deal with this environment. TheMedia Server Markup Language (MSML) was Convedia's solution, andMedia Server Control Markup Language (MSCML) was Snowshore's solution. Snowshore is now owned by Dialogic and Convedia is now owned by Radisys. These languages also contain 'hooks' so that external scripts (like VoiceXML) can run on call legs whereIVR functionality is required.
There was an IETF working group calledmediactrl ("media control") that was working on a successor for these scripting systems, which it is hoped will progress to an open and widely adopted standard.[5] The mediactrl working group concluded in 2013.[6]
