(none)

• Don Chamberlin (Almaden Research Center) contact
  
• Jerome Simeon (Watson Research Center, New York)

• Members of the W3C XML Query Working Group

• The Experts on XQuery: Views from the Working Group. (H. Katz, editor), Addison Wesley, 2004.
• XQuery 1.0: An XML Query Language. W3C Recommendation, 23 January 2007. See http://www.w3.org/TR/xquery.
• K. Beyer et al, "Extending XQuery for Analytics." Proceedings of the 2005 ACM SIGMOD Conference, Baltimore, June 2005.
• D. Chamberlin, "XQuery: An XML Query Language." IBM Systems Journal, Vol. 41, No. 4, 2002. See http://www.research.ibm.com/journal/sj/414/chamberlin.pdf.

Open standards are important to the software industry because they create markets in which many vendors can participate. They also promote the development of common tools and educational materials, and provide a focus for collecting user feedback and for controlling language evolution. The history of the database industry has provided many examples of the benefits of open standards.

The members of this project are participating in the W3C XML Query Working Group, a collaborative effort by several companies with a common interest in creating an industry standard for XML Query. The goal of the Working Group is to produce a standard XML query language that is widely implemented and used. If we are successful, the query language will be deployed in many environments, including database and content management systems, data integration and conversion tools, web service platforms, and service-oriented architectures.

Some properties of XML data that impact query language design include the following:

• It has an intrinsic order
• It is hierarchic
• It is self-describing
• It includes metadata as well as data
• It is often heterogeneous (varying in structure from one instance to the next)
• It is often sparsely populated
• Sometimes it conforms to a known schema and sometimes it does not

Some technical challenges in the design of an XML query language include the following:

• Merging facilities for structured query and unstructured search (approximate match, scoring and ranking) into a seamless language
• Striking a balance between static typing (when schema is known) and dynamic evaluation (when schema is unknown or heterogeneous)
• Maintaining a compatible relationship between XQuery and related standards including XML Schema, XML Namespaces, XPath, and XSLT
• Reducing the impedance mismatch between a declarative XML query language and a host programming language, which tends to add complexity to applications and to interfere with global optimization
• Defining appropriate interfaces for storage and retrieval of XML data in relational databases, including extensions to the SQL language standard (SQL/XML)

• XQuery Version 1.0 was published as a W3C Recommendation on January 23, 2007. The Recommendation includes a language syntax, a formal semantics specification, a data model, and a function library.
• W3C has also published a conformance test suite for XQuery, including more than 15,000 test cases. As of March 2007, fourteen XQuery implementations from various vendors have published their results against the conformance test, and eleven of these implementations have passed 98% or more of the test cases.
• The XML Query Working Group has been rechartered to create the following new language specifications during 2007-08:
• XQuery Version 1.1, including enhanced query features such as explicit grouping and error recovery
• XQuery Update Facility, including operators for insert, delete, update, and transform of persistent XML data
• XQuery Full-text Search Facility, including operators for stem matching, approximate search, scoring and ranking
• XQuery Scripting Extension, including facilities for development of applications for processing XML data using XQuery without relying on a host programming language