XML Schema

Appendix B. Work in Progress

Although W3C XML Schema was approved as a W3C Recommendation in May 2001, it is still just getting started. This chapter identifies a short list of schema-related projects that seem either promising, useful, or just on the way.

W3C Projects

Edited by the W3C, the W3C XML Schema is considered by the consortium to belong to the very foundation of XML—together with XML 1.0 and namespaces in XML—and it does impact virtually all the other XML specifications. The most heavily affected seem to be the triumvirate XPath/XSLT/XQuery (and by consequence, XPointer- and XPointer-based specifications), DOM, and RDF.

XPath, XSLT, and XQuery

One of the most amazing things about XPath and XSLT 1.0 is that queries and transformations can be executed by applications with no prior knowledge of the structure of the documents on which they work. This is a major difference from previous information systems, such as RDBMS, in which the layout of the tables needs to be defined before any query can be run. Even though this works just fine in many circumstances, there are two main areas in which improvements can be obtained if the structure of the instance documents is known.

The first of these areas is optimization. This is not crucial for small documents, but as soon as the size of the document grows (which is typically the case in a XML database), any optimizer will need food for thought to perform his job. The first piece of basic information that is required is about the structure ...