A key standard for building speech-based telephony applications, VoiceXML 2.0, received a final nod of approval from the World Wide Web Consortium last week.

Also: Technology Update - VoiceXML 2.0

The standard's official graduation comes just days before Microsoft is expected to formally launch its Speech Server products - which adhere to a competing standards effort - at the SpeechTEK conference this week in San Francisco.

The W3C advanced VoiceXML 2.0, along with the supporting Speech Recognition Grammar Specification (SRGS), to final "recommendation" status, effectively making them Web standards. These are the most mature of a handful of specifications in the W3C's evolving Speech Interface Framework.

The Speech Interface Framework aims to define a set of standards for building applications that let people interact with Web-based services over a telephone. The applications use a variety of voice-based interfaces that range from keypads and spoken commands to music and synthetic speech. Within the framework, VoiceXML controls how a voice application interacts with a user. Developers use SRGS to describe the words and phrases that end users are expected to give in response to spoken prompts.

Other elements of the framework include Speech Synthesis Markup Language (SSML), which is used for creating spoken prompts; Voice Browser Call Control (CCXML), which provides telephony call-control support for VoiceXML and other dialog systems; and Semantic Interpretation for Speech Recognition, which defines links between grammar rules and application semantics so that an application recognizes that two spoken variations of the same element, such as "Coke" and "Coca-Cola," should be treated as the same response.

VoiceXML, already is broadly adopted. It has become a standard scripting language for making Web content accessible via voice and phone - letting users make selections and provide information by talking instead of touching numbers on a keypad.

"VoiceXML allows users to create a description of a dialog between computer and user that can output text, graphics, synthesized speech, digitized audio - and also provide a means to recognize inputs from all these sources," says Ron Schmelzer, a senior analyst at ZapThink. "What makes VoiceXML cool is that you can specify an interface for application functionality that is not Web-based, but specify it in a way that allows Web developers to control how these voice-based application interfaces work."