XML Query Language (XQL)

Authors: Jonathan Robie, Joe Lapp and David Schach

The XML Query Language (XQL) is a notation for addressing and filtering the elements and text of XML documents. XQL is a natural extension to the XSL pattern syntax. It provides a concise, understandable notation for pointing to specific elements and for searching for nodes with particular characteristics. This proposal was provided in September 1998 to the XSL Working Group (http://www.w3.org/Style/XSL/Group/1998/09/XQL-proposal.html) as input when considering extensions to the XSL pattern syntax.

The companion document Querying and Transforming XML describes the benefits of basing query and transformation languages for XML on the XSL transformation language and the extensions to the pattern language proposed here.

Introduction
The XSL pattern language ( http://www.w3.org/TR/WD-xsl, section 2.6) provides an extremely understandable way to describe a class of nodes to process. It is declarative rather than procedural. One simply describes the types of nodes to look for using a simple pattern modeled after directory notation. For example, book/author means find author elements contained in book elements.

XQL (XML Query Language) provides a natural extension to the XSL pattern language. It builds upon the capabilities XSL provides for identifying classes of nodes, by adding Boolean logic, filters, indexing into collections of nodes, and more.

XQL is designed specifically for XML documents. It is a general purpose query language, providing a single syntax that can be used for queries, addressing, and patterns. XQL is concise, simple, and powerful.......

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