Multimedia Glossary: X

XHTML

Extensible HyperText Markup Language

W3C Recommendation 26 January 2000

XHTML can be viewed as HTML that is made XML-ready. In other words, it is HTML that complies with the strict rules of XML.

XLink

W3C Candidate Recommendation 3 July 2000

XLink is a linking mechanism related to the HTML linking (with the <a> element), but it is much more powerful. In HTML linking is one-directional, while XLinks can be multidirectional. HTML links can only be made to one link resource at a time, while XLink makes possible links to multiple resources. XLink relates conceptually to XPath and XPointer.

XM

MPEG-7

Experimental Model

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XML

Extensible Markup Language

W3C Recommendation 10 February 1998

XML is a subset of SGML and is a metalanaguage providing the rules and conventions to be used to create other languages following these rules. These other languages are called XML-applications. There are thousands of XML-applications such as MathML (Mathematics Markup Language), CML (Chemical Markup Language), CDF, OSD, HDML (Handheld Device Markup Language), RDF (Resource Description Framework), MML (Music Markup Language) - see Robin Cover's XML pages for a complete list (http://www.oasis-open.org/cover/sgml-xml.html).

XML documents can be created with a text-editor just like HTML documents. XML, however, is much stricter with its rules. XML documents need to be well-formed (e.g. element names, i.e. tags, are case sensitive and must be ended, unlike HTML) and for data vailidity they also need to be valid (i.e. be associated with a DTD which contains definitions of and relationships between elements).

XPath

W3C Recommendation 16 November 1999

XPath provides the syntax and data model to address segments of an XML document. Conceptually it relates to DOM as objects in a document are regarded to have family relationships such as parent, children and siblings. With XPath the nodes between family members can be accessed and manipulated. XPath can be thought of as the path that should be followed to reach a target. XPath relates conceptually to XLink and XPointer.

XPointer

Candidate Recommendation 3 July 2000

XPointer provides a standard manner for identifying document fragments. XPointer also relates to DOM by operating on the abstract document objects rather than on the XML syntax itself. XPointers can be thought of as points in the document that function as targets. XPointer relates conceptually to XLink and XPath.

XSL

Extensible Stylesheet Language

W3C Working Draft 21 Apr 1999

XSL is a style sheet language based on the principals of XML and more powerful than CSS. XSL consists of two main components: XSLT (which concerns the document tree) and formatting (which is based on CSS 2.0).

XSLT

XSL Transformations

W3C Recommendation 16 November 1999

XSLT is a transformation language to change an XML document into another. It operates on the document tree (related to DOM) and is a sub-section of XSL, although it can operate independently from XSL. XSLT is obviously not as powerful as programming languages to change documents, but as it is an XML application, it follows the same rules as any XML-based application and can be created with a simple text-editor.

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