W3C Publishes Eight New XML-Family Specs

XPath, XSLT graduate to version 2; XQuery joins the class

By David Worthington

February 15, 2007 —

Two World Wide Web Consortium working groups late last month gave XQuery, XSLT 2.0 and XPath 2.0 their stamp of approval to jump-start enterprises’ efforts to link databases onto the Web and steer the convergence of databases with document systems.

Although XQuery, XSLT (Extensible Stylesheet Language Transformation) 2.0 and XPath (XML Path Language) 2.0 are the primary standards, five more were adopted concurrently as supporting technology in the XML family, with the aim of providing new ways to access, convert and query XML documents and data. “These specifications provide a much needed bridge between two worlds: documents with complex but irregular internal structure on the one hand, and databases and simple data with atomic values on the other,” explained W3C’s Michael Sperberg-McQueen, a contributor to the original XML 1.0 specification.

XQuery is the brainchild of industry luminaries Don Chamberlin, an IBM research fellow and co-inventor of SQL, and Jim Melton, Oracle’s chief standards architect. XQuery is designed to do for XML what SQL did for relational databases: provide a unified interface for accessing data from multiple sources. To that end, it has facilities to query both structured and semi-structured data that is unconstrained by schemas. Vendors of relational databases, middleware and XML-native database systems, as well as numerous open source projects, are early adopters of XQuery.

XSLT 2.0 extends XSL transformation capabilities beyond the original specification with an enlarged library of functions that maintains most backward compatibility. New grouping and aggregation options have been added.

The spec’s authors claim that sifting out errors is demonstrably easier, due in large part to data conversions between XML schemas. This is an optional function that can reduce both runtime and compile time errors.

XSLT 1.0 has been widely used in browsers and Web servers since it was first introduced in 1999. Enterprises and developers began to adopt primitive versions of the specification as it was milled out—going back to 2002. W3C claims that there have been in excess of 150,000 downloads of XSLT 2.0 implementations, many already in use within production environments.

W3C describes XPath 2.0 as a superset of the original language. Likewise, it is a subset of XQuery and XSLT 2.0. New functions provide more robust text processing capabilities using regular expressions; path expressions now support conditional statements. The updated specification supports more data types than before, extending XPath’s ability to process information.

“XPath is widely regarded as the standard mechanism for locating objects in XML,” Chamberlin told SD Times. “The fact that this is adopted in common for XSLT and XQuery is very important to the industry because these have become a suite of standards and are converging into a compatible family.”

X MARKS THE SPECS
The remaining five recommendations complement the others at a lower level; the awkward naming convention reflects their use in combinations of XPath, XQuery and XSLT. XQuery 1.0 and XPath 2.0 Data Model is the data model set for all three of the “major” standards. XML Syntax for XQuery 1.0 is an XML syntax for XQuery that can be parsed by programmers, but is primarily machine-processed.

XQuery 1.0 and XPath 2.0 Formal Semantics describes the “meaning” of the namesake standards. XSLT 2.0 and XQuery 1.0 Serialization was published to describe the serialization of the data model into octets for use with other applications. The descriptions of the functions, operators and constructors used in XPath 2.0 and XQuery are given in the XQuery 1.0 and XPath 2.0 Functions and Operators Version 1.0 recommendation.

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