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The W3C XPath Recommendation The XPath query language recommendation originated from two separate W3C initiatives called XSL and XLink. In early 1999, the W3C’s XSL working group (WG) was developing XSL Transformations (XSLT), a language to describe tree transformations of XML documents. XSLT development included the task of how to specify certain parts of an XML document to be transformed. Parallel to this, the XLink WG was developing means to point from one XML document to another XML document. In an attempt to synchronize their activities, the two groups jointly worked upon a standard means to do their common pointing. Since it became a W3C recommendation in October, 1999, XPath has gained enormous popularity and has been implemented in many XSLT processors (James Clark’s XT and Michael Kay’s SAXON). Because of the almost universal acceptance of XPath, Tamino X-Query contains almost the complete XPath scope, with the exception of XPath’s "axes" concept. XPath is not a true query language, however, because it lacks several features that are required for querying, e.g. add, delete, update, insert, join, sort. Tamino’s X-Query has therefore been enriched with some appropriate XQL mechanisms, e.g. sort, and some proprietary add-ons in the field of data-indexing and text retrieval. For retrieval, for example, X-Query provides an additional match operand (~=) that is similar to XPath’s equal (=) for strings, but normalizes, understands wildcards, and looks up words in sentences. Here is an example of an X-Path query. XQL influences W3C standards Another W3C effort that influenced the development of X-Query is the XML Query Language (XQL). Originally called XQL98, XQL was first proposed to the W3C in September 1998 by Jonathan Robie (Software AG), Joe Lapp (webMethods, Inc.) and David Schach (Microsoft Corporation). XQL strongly overlaps with XPath ideas and methods, and the syntax is similar. But the two standards differ in the way they view XML. XSL and XLink are mostly document-centered, inferring that an XML document is mostly text. This stems from XML’s SGML origins and is reflected, for example, in the DocBook DTD created by Norman Walsh. The XQL movement, however, views XML from the database perspective. In this light, an XML document is referred to as "XML data" and terms foreign to the "document" world, such as "join" or "grouping," are mentioned. The "position" issue reveals the different views taken by XPath and XQL. A position is used to specify the location of elements in an XML structure, which can be pictured like a tree with branches. From a XQL or "database" point of view, the first branch (or, in technical terms, the first child of a parent) has the position "zero." This is because most programming languages use the index beginning with "zero." But XPath indexes branches beginning with "one;" no self-respecting author would refer to the first chapter of a book as the "zeroth." XML Query Language and Quilt XQL, which still exists as a separate standard in its latest version XQL99, has influenced the development of other standards. Firstly, XQL has already left its footprint in the two documents the XML Query WG has released so far, i.e. the Query Requirements Document and the Query Data Model. XQL has also influenced the development of Quilt, a new XML query language suggested to the Query WG in a proposal by the top guns in the database query field. These are: the author of XQL, Jonathan Robie (Software AG), one of the authors of SQL 2, Don Chamberlin (IBM) and an author of XML-QL, Daniela Florescu (INRIA), in March 2000. Quilt comes the closest to what can be referred to as a global query language, because it combines a number of XML query approaches, the most influential ones being XQL and XML Query Language (XML-QL). XML-QL was first suggested as a W3C Note in August, 1998. This approach favored an SQL-like query syntax which looked rather different from XQL’s XPath-like syntax. The combination of these two ideas under the new Quilt roof appears very promising. Quilt is still in draft form, and will certainly go through many changes before it becomes a recommendation. Several of the concepts from XQL have also found their way into the XPath Working Draft, mainly due to the fact that Jonathan Robie is also a member of the XSL WG. In November 1999, XPath became a "W3C Recommendation," the highest status a "standard" can achieve within the W3C. In September 1999, the W3C’s XML query WG was constituted, and XQL served as one of the main design inputs for the WG’s work. For more information about the Tamino XML database, see http://www.softwareag.com/tamino
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X-Query: A universal query interface for XML