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XQuery is the big fish in a pond full of related standards, such as XSLT (Extensible Stylesheet Language Transformations), a W3C language designed by James Clark and the XSL Working Group. While there is some overlap between the XSLT and XQuery, XSLT was designed as a style-sheet language for performing transformations of documents into XML and other formats whereas XQuery's mission has been to replicate what SQL does, but for XML data.

Along with the W3C's standards efforts around XQuery, another important emerging standard is JSR (Java Specification Request) 225: XQuery API for Java, or XQJ. Sponsored by IBM and Oracle, JSR 225 will provide XQuery-standard methods for XML data access in much the same way that JDBC (Java Database Connectivity) did for accessing, querying and updating relational databases.

SOA (service-oriented architecture) approaches are also dependent on XML. Thus, it comes as no surprise that the RDBMS vendors are working quickly to maintain their relevance in an XML-dominated world. The XQuery standard is crucial to all, so its evolution may be smoother than other industry standards, including SQL. Nonetheless, distinctions will always exist between data sources--database and middleware vendors will succeed if they can ease developers' current XML data-integration headache of having to learn and implement a series of APIs for each data source and writing lots of procedural code.

XQuery's primary drawback right now is simple--immaturity. It provides read-only access to XML data and lacks support for analytics and BI. However, updating and other functions will be added over time--the popularity of search engines will likely speed its build-out toward providing extensions that give finer control over full-text searches.

XQUERY AND SQL

A discussion about XQuery wouldn't be complete without touching upon SQL. SQL can access and manipulate data organized in relational tables: Normalization, primary key relationships and indexes determine the data that a SQL query will return efficiently.

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XML is all about exposing data so it can be reused. Hierarchies and sequential relationships between documents and parts of documents are also important, so XQuery functions must enable different operations than SQL. To accomplish this, XQuery and XSLT working groups will have to sort out functionality; competition between these efforts could hamper development.

XQuery will never replace SQL because most business data is perfectly happy being stored and accessed through the relational model. XQuery is focused on the burgeoning world of XML documents, and content and collaboration through interchange of these data sources; vendors know they will cease to be relevant if they can't provide technology for these purposes. Still, it remains an open question whether RDBMS vendors can deliver XQuery and XML functionality with SQL-like subsecond response times. If they stall in providing this performance, customers will address their XML data-management woes with pure-play, custom-built or middleware-oriented solutions.

David Stodder is editor in chief of Intelligent Enterprise, a sister CMP publication. Write to him at dstodder@cmp.com. Ben Dupont is a systems engineer for Wps Resources in Green Bay, Wis. He specializes in software development. Write to him at bdupont@nwc.com.

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