XQL (XML Query Language)

XQL (XML Query Language) is a way to locate and filter the elements (data fields) and text in an Extensible Markup Language (XML) document. XML files are used to transmit collections of data between computers on the Web. XQL provides a tool for finding and/or selecting out specific items in the data collection in an XML file or set of files. It is based on the pattern syntax used in the Extensible Stylesheet Language (XSL) and is proposed as an extension to it.

The XSL pattern language is a declarative way to indicate specific elements for processing. It uses simple directory notation. For example, book/author  means: Select all author elements in all book elements in a particular context (for example, within an XML file or a set of files). XQL adds to this directory pattern notation the ability to use boolean logic, to filter out elements, to index into a collection of elements, and to do some other things. Using XQL, a program could be written to search repositories of XML files, to provide hypertext links to specific elements, and for other applications.

For more information, we recommend reading the XQL proposal at the World Wide Web Consortium (W3C) Web site.