XML Query Languages
A number of query languages exist today. All were developed to solve one problem or another. None solve all the problems or fit all the requirements previously discussed. In fact, there are a number of competing mechanisms for processing queries. In the remainder of this section, we will look at several different query languages and see how they attempt to achieve the goals and fit the previously mentioned requirements.
XML-QL
XML-QL, or the XML Query Language, is a query language submitted to the W3C by Microsoft, Texcel, and webMethod. At its simplest, XML-QL is seen as a superset of XSL. XML-QL query statements always take the form
WHERE XML-QL pattern CONSTRUCT output
pattern matches a given portion of an XML document ...
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