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Excerpt: Early Adopter VoiceXML: VoiceXML with XSLT (HTML and WML), Part 2

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Generating MyRubberbandsML

Now we have examined the existing database, outlined a suitable voice interface for it, and defined our source markup language and the method for generating it. Now, we are ready to create a stylesheet to convert it to a VoiceXML form implementing the design we decided on in the previous section Designing A Voice Interface. This stylesheet, myrubberbands2vxml.xsl, is quite lengthy, and can be found in its entirety in the code download. Here, I shall pick out just the important points in the code for discussion; including the dynamic generation of grammars, some VoiceXML features worthy of particular attention, and fundamental XSL concepts used.

VoiceXML Stylesheet

Note that the stylesheet is designed to produce a single VoiceXML document containing just one user's data. So, its top-level template only matches documents where the top-level attribute export_type is set to single. The indent attribute on the <xsl:output> tag will produce a well- formatted result document that will be easier for a human brain to examine.
<?xml version = "1.0"?> 
<xsl:stylesheet xmlns:xsl=
"http://www.w3.org/1999/XSL/Transform" version="1.0"> 
<xsl:output method="xml" encoding="ISO-8859-1" indent="yes"/> 
<xsl:template match=
<vxml version="1.0"> 
<meta name="author" 
content="Underpaid Myrubberbands Engineer"/> 
<meta name="copyright" 
content="Copyright (C) 2001 Myrubberbands.com"/>
The next block illustrates one way XSL can generate elements with an attribute having dynamic content: the <xsl:element> construct.

<xsl:element name="meta">   
<xsl:attribute name="name">description
<xsl:attribute name="content">Voice Interface for #
<xsl:value-of select="customer/@id"/>   
We will need to set up some variables for use in the VoiceXML document. First off, we grab the user's Automatic Number Identification (ANI) and Dialed Number Identification Service (DNIS) for later use. These correspond to the phone number that originated the call (analogous, but not identical to, the consumer caller ID service) and the number that the user dialed. The implementation of these is system dependent, and the data may not be available for all calls in any case. They are included here mainly for illustration. In a real application, the ANI can be used for auto-identification of the user.

The form_pointer variable will be used for navigation later.

<var name="customer_ani" expr="session.telephone.ani"/> 
<var name="customer_dnis" expr="session.telephone.dnis"/> 
<var name="session_error_count" expr="0"/> 
<var name="form_pointer" expr="'mainMenu'"/> 
<var name="user_command" expr="''"/>

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This article was originally published on February 14, 2002

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