World Wide Web Consortium Issues XPointer Recommendation

Author(s) and publish date


XPointer Gives Extensible Model for Identifying XML Fragments, Improving Precision of Linking -- 25 March 2003 -- Today, the World Wide Web Consortium (W3C) issues the XML Pointer Language (XPointer) Recommendation - the XPointer Framework, the XPointer element()Scheme, and the XPointer xmlns() Scheme. The XPointer Framework provides a lightweight extensible model for identifying parts of XML documents. The XPointer element() scheme allows the user to point to specific elements in XML documents and data, while the XPointer xmlns() scheme brings the power of XML Namespaces to the XPointer Framework, giving a way to avoid name collisions between schemes and provide namespace binding information for use within other schemes.

Advancement of these documents to Recommendation indicates that these W3C-developed specifications are stable, contribute to Web interoperability, and have been reviewed by the W3C Membership, who favor their adoption by the industry.

Identifying Parts of XML Documents Had Shown Limitations

When XML 1.0 was first issued as a W3C Recommendation in 1998, it included a feature called "id," which gave authors a method for identifying a specific part of a XML document in conjunction with anchors and other xml elements. However, this meant that parts of a document could only be formally identified by the author of the document, not by other users who might want to reference a particular section or fragment without an id.

The W3C XML Linking Working Group, along with the W3C XML Core Working Group, began working on ways to expand the power of linking to and identifying XML fragments. Their combined results include the W3C XML Linking Recommendation, the W3C XML Base Recommendation, and now, XPointer.

XPointer Framework Expands "Pointing" and Linking Capabilities

The XPointer Framework consists of a set of basic set of syntax rules for identifying parts or fragments of XML. It provides the mechanism essential for more full and rich implementation of XML Linking. One can still use ids as pointers into XML documents and data, but the XPointer Framework also permits new XPointer schemes for identifying XML fragments. The rules for how these XPointers are created are consistent with XML syntax. The XPointer Framework also lives up to the "Extensible" in XML, as it allows users to create and reference their own schemes.

XPointer element() Scheme Makes Simple, Elegant Use of XML Document Structure

The XPointer element() scheme allows pointers to be made from some of the most common components of XML documents and data - namely elements. The element scheme allows for both the use of ids and the use of a list of "pointer-parts" - numerical and text expressions which guides a software processor to a precise XML fragment.

XML Namespace Scheme for XPointer Helps Avoid Name Clashes

The Namespaces in XML Recommendation helped developers and applications identify XML Languages and make them easier to combine, eliminating both conflict and ambiguity. The XPointer xmlns() scheme serves the same purpose within XPointer.

As XPointer schemes are independently developed, the use of the XPointer xmlns() scheme distinguishes one scheme from another in a definitive manner. Even if the same name is used in two or more XPointer schemes, namespaces enable a processor to tell the difference, and process the XPointer correctly. The XPointer xmlns() scheme also makes XPointers to be self-contained, even if they involve prefixed names which require namespace declarations for their interpretation.

Extensible Framework Makes Room for New Schemes

Beyond the two W3C XPointer Schemes published today, other schemes developed either inside or outside of W3C Working Groups may also be used in conjunction with the XPointer Framework, provided the simple guidelines for the Framework are followed.

Another XPointer Scheme under development at W3C is the XPointer xpointer() Scheme, which relies on the W3C XML Path Language (XPath 1.0) Recommendation. The XPointer xpointer() Scheme is currently a W3C Working Draft.

XPointer Framework Developed by IT Industry Leaders and XML Experts

The XML Linking Working Group produced these W3C XPointer Recommendations. It consisted of invited experts from the research community and information technology leaders from AOL/Netscape Communications; Arbortext; Fujitsu; Microsoft Corporation; Oracle Corporation; Reuters; Sun Microsystems; the University of Edinburgh; and the University of Southhampton.

About the World Wide Web Consortium [W3C]

The W3C was created to lead the Web to its full potential by developing common protocols that promote its evolution and ensure its interoperability. It is an international industry consortium jointly run by the MIT Laboratory for Computer Science (MIT LCS) in the USA, the European Research Consortium for Informatics and Mathematics (ERCIM) headquartered in France and Keio University in Japan. Services provided by the Consortium include: a repository of information about the World Wide Web for developers and users, and various prototype and sample applications to demonstrate use of new technology. To date, nearly 430 organizations are Members of the Consortium. For more information see


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