Visual AJAX != Voice AJAX

There is an interesting article in the latest installment of Speech Technology Magazine ““ Jim Larson offers his thoughts on the use of the AJAX development technique in VoiceXML applications.

Larson points to a notable example of “AJAX-like” programming in VoiceXML. In fact, its one I have commented on before. My view of this technique hasn’t changed. It’s powerful, but it isn’t AJAX.

The way I view AJAX programming, there are two key hallmarks; processing of XML on the client using JavaScript and the DOM, and asynchronous communication with a back end server using HTTP. The approach referenced by Larson includes the former, but misses the latter.

Make no mistake, using the new [VoiceXML 2.1 element]( to fetch an XML document that can be utilized from within a VoiceXML script without a page transition is indeed handy. But there isn’t any asynchronous communication happening here "“ the external XML document is fetched only once, [typically at the begining]( of script execution. For asynchronous behavior, we need to look to one of VoiceXML’s sister technologies "“ the [Call Control eXtensible Markup Language]( (CCXML).

The CCXML 1.0 specification (a last call working draft from the W3C) includes the [ element](, which allows a developer to throw a user defined event that can be caught by the initiating (or another) CCXML document. The classic example involves the throwing of a "timesUp" event that allows a developer to designate when a call should be terminated.

The good folks at Voxeo (leaders in the effort to formalize the CCXML standard) have added functionality to their platform that allows the element to asynchronously [send and receive information via HTTP]( So its theoretically possible to construct a conference call application that sends a message to a back end script to kick off an IM message to the call organizer when there are 30 seconds left on the call. (Actually, that sounds pretty cool "“ may have to try that one soon.)

When it comes to AJAX in VoiceXML, the same functionality is generally available but the needs of developers are somewhat different. Callers to a VoiceXML application probably don’t perceive page transitions in the same way that users of a visual web application do. VoiceXML has fetching and caching functionality built into it that can be used to manage the delay between page transitions. It’s probably a better use of developer time to understand fetching and caching more intimately than to try and replicate AJAX in voice applications.