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As more and more information is either stored in XML, exchanged in

XML, or presented as XML through various interfaces, the ability to

intelligently query our XML data sources becomes increasingly

important. XML documents are structured documents ?they blur the

distinction between data and documents, allowing documents to be

treated as data sources, and traditional data sources to be treated as

documents. . XQL is a query language designed specifically for

XML. In the same sense that SQL is a query language for relational

tables and OQL is a query language for objects stored in an object

database, XQL is a query language for XML documents. The basic

constructs of XQL correspond directly to the basic structures of XML,

and XQL is closely related to XPath, the common locator syntax used by

XSL and XPointers. Since queries, transformation patterns, and links

are all based on patterns in structures found in possible XML

documents, a common model for the pattern language used in these three

applications is both possible and desirable, and a common syntax to

express the patterns expressed by that model simplifies the task of the

user who must master a variety of XML-related technologies. Although

XQL originated before XSL Patterns, there were strong similarities

between the two languages, and we have adopted XPath syntax for the

constructs which differed. Not all constructs found in XPath were

needed for queries, and some constructs used in XQL are not found in

XPath, but the two languages share a common subset. . The XQL

language described in this paper contains several features not found in

previously published versions of the language, including joins, links,

text containment, and extensible functions. These new features are

inspired in large part by discussions stemming from the W3C QL '98

Workshop, and make it possible to combine information from

heterogeneous data sources in powerful ways. Great care has been made

to maintain the fundamental simplicity of XQL while adding these

features. . This paper is intended as input for the upcoming W3C Query Language Activity, and for the further development of XPath. . Buy Book at Lowest Price on Amazon

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