One recently established standard is [SALT], which extends existing Web markup languages to enable multimodal (speech plus other modalities) and telephony (speech only) access to the Web. It is thus superior to the earlier standard VoiceXML—a different programming language supporting only telephony interaction for call center speech applications.

The W3C just advanced VoiceXML 2.0 to Recommendation in March, and have begun work on VoiceXML 3.0. While SALT was submitted to the W3C, it is not on the standards track.

VoiceXML has huge industry momentum. There are thousands of commercial VoiceXML applications running worldwide on platforms from nearly 100 vendors. VoiceXML applications serve all industries, not just call centers, and range in size up to massive ones like the North American 1.800.555.1212 business directory service. There are at most a handful of commercial SALT applications. Four SALT Forum companies recently joined the VoiceXML Forum board, and of the 59 SALT Forum companies making recent commercial announcements, 73 percent made substantial bets on VoiceXML.

VoiceXML is suitable for multimodal interactions. The X+V language (www.w3.org/TR/xhtml+voice) uses standard W3C mechanisms to compose XTHML and VoiceXML into a multimodal markup language. X+V is based on the elegant model-view-controller paradigm, making it well-suited to a broad range of architectures, and able to include other modalities (e.g., pen) seamlessly. SALT bundles everything into a mass of complex Javascript. A growing number of companies are working with X+V, including Access, IBM, Kirusa, Motorola, NewportWorks, Openstream, Opera, Real Soft, SAP, and V-Enable.

SALT's heavy dependence on JavaScript make even small examples from the SALT 1.0 specification 3-5 times larger than the corresponding VoiceXML (see www.voicexml.org/faqs.html). SALT developers need to worry about low-level concerns — like "hanging" dialogs (SALT 1.0, Section 2.6.5) — that can't happen in VoiceXML. All of SALT's extra programming increases development time and cost, even when it is authored indirectly by tools like servlets and JSPs.

VoiceXML's wide acceptance as a standard, huge industry uptake, suitability for multimodal interaction, and higher developer productivity clearly demonstrate its superiority.

VoiceXML Forum Technical Council (www.voicexml.org)
Piscataway, NJ