XML: the next generation

Some of the W3C's work on XML will have a direct impact on the way we use the Web.

Last week I noted how the World Wide Web Consortium's (W3C) work on XML was probably its most significant contribution to the online world, at least in recent years. That commitment was underlined with the release of the XML Conformance Suite. According to the accompanying press release, the suite consists of more than 2,000 test files for establishing the conformance of code to the XML 1.0 (Second Edition) standard.

Just as important as this bolstering of current standards is the work driving them forward. It is hard to tell from the rather muddled XML activity statement, but the W3C is very productive here. Some of this work seems rather specialised, like the XML Schemas, although the extent of Robin Cover's XML Schemas links suggests that this is a subject of lively interest to those in the field.

For the rest of us, three other areas look likely to have a more immediate impact on the way we use the Web, especially in business. The first of these is the Extensible Stylesheet Language (XSL). This is a good example of how far the W3C has moved on since the early days of XML.

XSL was originally designed as a way of applying a stylesheet to a general XML file to produce another file, for example HTML, for display in a browser. In this respect, it was very similar to the W3C's other stylesheet standard, Cascading Style Sheets (CSS), and the resulting confusion forced it to explain why two such standards were needed.

But XSL has moved on, and now consists of three parts a href="http://www.w3.org/TR/xslt" >: XSL Transformations (XSLT), which handles the transformation of one XML file into another; XML Path Language (XPath), which is a language used by XSLT to access or refer to parts of an XML document; and XSL Formatting Objects, which handles the actual formatting. Much more about this increasingly rich area can be found in Robin Cover's pages devoted to the subject.

The XML trio of XML Pointer (XPointer), XML Base and XML Linking (XLink) are about creating a kind of generalised hyperlink in XML documents.

XLink allows elements to be inserted into XML documents in order to create and describe links between resources. As well as the simple unidirectional kind of links found in HTML documents, other, more sophisticated variants are also possible.

XPointer allows the internal structures of XML documents to be addressed (and external ones, too), and builds on XPath, which is also used by XSL Transformations. Once again, Robin Cover's resources provide invaluable help in disentangling what are a complex and intertwined set of standards.

The third area where the W3C is doing some potentially important work is that of XQuery. This is a query language for XML documents that is designed to bridge the gap between the worlds of traditional databases and online documents. The kind of situations where XQuery might be used are illustrated in a background paper from the W3C.

It is striking that already a number of commercial products support XQuery. The presence of both Oracle and Microsoft hints at great things for this nascent technology. More background is available from the relevant page from Cover.

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This was first published in July 2002


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