XML supplements Web content with "meta information," self-descriptive labels for each piece of text that goes wherever the document goes. This turns each Web document into a self-contained, mini-repository, and positions the XML specification as the most fundamental standard and building block for XML and Web services technology platforms.

Location: XML 1.0 (third edition)
Organization: W3C
Location: XML 1.0 (namespaces)
Organization: W3C
Location: XML 1.1
Organization: W3C>
Location: XML 1.1 (namespaces)
Organization: W3C

Within just about any application design, there will be a requirement for the format of data to be altered between the time it is first retrieved, to when it reaches its final destination. Because XML provides a clear separation of content, structure, and presentation, the output format of an XML document can be completely transformed. XSLT performs two primary types of XML transformation: the structural conversion of one XML document type into another, and the aesthetic formatting of an XML document into human-readable output.

Location: XSLT 1.0
Organization: W3C
Location: XSLT 2.0
Organization: W3C
Location: XSL 1.0 (includes XSL-FO)
Organization: W3C
Location: XSL 1.1 (includes XSL-FO)
Organization: W3C" target="_parent">W3C

By abstracting certain utility functions, a relatively modular set of XML specifications has emerged. Functional redundancy is avoided by allowing these supplementary features to be reused by other standards. XPath is an example of such a utility specification. It can be used independently within custom programming logic to interact directly with the XML Document Object Model, or it can be intrinsically incorporated within other specifications. Essentially, XPath provides an expression syntax used to create location paths.

Location: XPath 1.0
Organization: W3C
Location: XPath 2.0
Organization: W3C

The XQuery specification establishes a comprehensive data query language, designed specifically for XML documents. XQuery is aligned (and overlaps considerably) with release 2.0 of the XPath specification. XQuery uses the XPath language to define data source addressing, and even adds some new XPath extensions.

Location: XQuery 1.0
Organization: W3C
Location: XQuery 1.0 and XPath 2.0 Data Model
Organization: W3C

XSD is a comprehensive data modeling language for XML documents, and the one XML schema specification that has received the broadest industry support across contemporary XML and Web services technologies.

Location: XML Schema Part 0 (primer)
Organization: W3C
Location: XML Schema Part 1 (structures)
Organization: W3C
Location: XML Schema Part 2 (data types)
Organization: W3C