W3C mulls XML spec

A specification being considered by the World Wide Web Consortium today seeks to soup up XML.

The W3C today acknowledged the specification's submission by IBM and Microsoft. The next step is for the W3C to decide whether to recommend the specification. W3C recommendations are not legally binding but are widely respected in the Net community.

The specification, known as the Document Content Description for XML, outlines how authors of XML-based languages define and structure the tags within their documents. DCD, if adopted, would supersede the current method for describing XML documents, which is known as the DTD, or document type definition.

XML, which stands for extensible markup language, is a W3C recommendation that lets Web developers create tags specific to their own industries and interests. MathML, for example, features tags that are specific to mathematical functions.

The advantage of XML is that anyone can designate his or her own tags. But browsers have to have some way of knowing what they mean. The task of educating browsers on the fly currently falls to DTDs, which the XML document can either link to or include within the body of its text.

DCDs improve on DTDs in the following three principal ways:

Unlike the DTD, the DCD provides the ability to specify data types. For example, if the value, or content, of a tag is the number 120874, a DCD will let the developer specify whether that number is a date, a time, a time interval, a Boolean value, an integer, a decimal, or some other type of data.

DCDs will let authors create open content models. The way it is now with the DTD's closed model, an author cannot add tags to a completed DTD. But the DCD will let authors carve out a space for additional tags to be specified at some point in the future.

DCDs allow new flexibility in letting developers reuse tags. For example, an invoice written using XML could reuse an address tag set within the document. Another XML document also could use that tag set. Neither of these capabilities exist with the current DTD.

DCDs are XML documents; DTDs are written in a different syntax.

DCDs and DTDs alike fall under the W3C's work in metadata, or data that describe other data. Another, more general, movement within the W3C's metadata push is the resource description framework, or RDF. The DCD relies on work accomplished in the RDF and XML working groups, according to IBM, and addresses goals specified by those groups.

David Fallside, IBM's representative to the XML working group, lauded the submission as a crucial improvement to the XML landscape.

"For things like e-business applications, things like data-typing are absolutely critical," Fallside said. "You have to have it when sending an XML document between applications. People have been crying out for data-typing in XML. So long as it was just being used in browsers, it wasn't much of an issue, but when you're trying to build business applications that are passed back and forth, it's really critical in order to effectively use XML."