Core Standards

The core standards category is composed of the original XML 1.0 specification and the rest of the fundamental standards that are logically bound to it. Taken as a group, these standards form the foundation on which new standards and applications can be built. They are relatively stable and are widely supported by XML parsers and tools.

XML 1.0 Recommendation

This is the specification of the XML language itself. It lays down the rules for how XML documents can be constructed, how they can be validated (using the Document Type Definition method), and how they can be encoded using various character sets. All other standards and applications either extend or depend on this specification.

Namespaces in XML

In a perfect world, Namespaces in XML would have been incorporated directly into the XML recommendation itself. But, in the interest of market timing, the W3C wisely decided to release XML 1.0 without namespaces. Namespaces provide support for mixing the vocabularies from multiple XML applications together in a single document.

XPath

Many tools and standards that are intended to manipulate XML documents (XSLT, XML Schemas, and so on) need to be able to identify locations within and select portions of XML documents. Just as the Structured Query Language (SQL) supports selecting values from relational database systems, XPath supports selecting data from XML documents.

XBase

This is a very short recommendation that defines a special attribute called xml:base. This attribute serves the same purpose as the <base> element in HTML, which is to override the default base for relative URLs with an explicit base.

XLink

Because XML is intended to serve as the foundation for the next-generation “semantic web” on the Internet, hypertext linking is a critical piece of functionality it must support. The XML Linking Language effort is an attempt to define a comprehensive hypertext linking system that can be incorporated into any XML application. At the time of this writing, it has not yet been approved as an official W3C recommendation, but its use is already anticipated by standards such as XHTML.

XPointer

The XLink standard focuses on linking various documents together. The XPointer standard deals with locating single points or ranges within a document. It defines how XPath expressions may be used to locate XML document nodes.