First Words

Welcome to “First Words” – the VoiceXML Review’s column to teach you about VoiceXML and how you can use it. We hope you enjoy the lesson.

Metadata

Overview

By the time you read this, VoiceXML 2.0 will have been published as a Proposed Recommendation by the W3C. Congratulations to all those who have enabled this to happen!

First, we’ll cover a little history. VoiceXML 1.0 included the <meta> tag, allowing the attachment of ‘meta’ information to a VoiceXML document. Metadata provides information about the document itself, rather than the content of the document.

The <meta> tag allowed the application developer to associate information with the document itself, in the form of a name-value pair. Some typical examples of use of the <meta> tag included:

<meta name=”author” content=”Rob Marchand”/>
<meta name=”maintainer” content=rob@example.com/>

The former usage would specify (obviously) the author of the document, and would likely not have any other purpose. The latter usage specifies the maintainer of the document; typically an e-mail address to which errors and warnings related to processing of the document would be reported.

VoiceXML 1.0 further supported the ‘http-equiv’ form of <meta>, allowing the document author to provide an HTTP header in the returned document. For example, to control document expiration, one might use the following <meta> tags (this example is drawn from the VoiceXML 2.0 specification):

In this example, the document itself specifically requests that it not be cached. Note that only one of http-equiv or name can be specified. Otherwise the interpreter platform must throw an error.badfetch event.

VoiceXML 2.0 continues to support <meta> - however, it is recommended that the document authors use the <metadata> element in it’s place. The <metadata> element allows authoring of a structured set of document metadata, as defined by an XML schema. The <metadata> element allows for much richer structured data to be attached to the document.

The <meta> and <metadata> tags are valid as a child of the top-level <vxml> document element.

It is recommended that the <metadata> element contain information specified in the syntax defined by the Resource Description Framework (RDF). The VoiceXML specification further recommends that the actual information represented in RDF reflect that required by the so-called “Dublin Core” metadata initiative. Dublin Core defines a set of recommended metadata that should be used in web documents.

The following Dublin Core metadata properties are recommended in <metadata>:

· Creator - An entity primarily responsible for making the content of the resource (a company or individual)
· Rights - Information about rights held in and over the resource (for example, a copyright statement)
· Subject - The topic of the content of the resource.

Here is an example from the VoiceXML 2.0 specification, showing how <metadata> can be used to include RDF format document metadata in a VoiceXML document:

Now, you might say to yourself that this is quite a mouthful. However, it is anticipated that much of this information will be generated automatically (by a tooling environment for example). The benefit is the use of a standard mechanism for storing metadata within an XML document, allowing more general metadata tools to be used for indexing and document manipulation. Examination of the information in the above example shows a great deal of information regarding the document, and reflects the often-rich structure of such information. RDF provides an extensible framework for the representation of such information, and further meets the W3C purpose of standards reuse as part of specification development.

Summary

It is interesting to note that SRGS grammars, and SSML speech markup can both contain <meta> and <metadata> components, just as VoiceXML documents can. In fact, the <metadata> mechanism is supported in other W3C languages, including HTML. For further details regarding the use of <metadata> you might want to have a look at:

- Resource Description Framework - http://www.w3.org/TR/REC-rdf-syntax/
- Dublin Core Metadata Initiative - http://purl.org/DC/

This month, we’ve talked a little about the use of metadata as part of your VoiceXML document. Next month, we’ll look at some of the additional clarifications and tweaks made as part of the migration of VoiceXML 2.0 to Proposed Recommendation.

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