Electronic Dissertations Library

XML: the future of web markup?, by Elliot Pritchard

XML TUTORIAL - ASSOCIATED SPECIFICATIONS

XSL (eXtensible Stylesheet Language) stems from two pre-existing standards: DSSSL (Document Style Semantics and Specification Language) and CSS (Cascading Style Sheets). Whereas XML describes information, XSL determines how it should be presented. It performs two main sub-processes. Firstly, there is the process of 'tree transformation', where the 'logical tree structure' of the XML document is transformed into a result tree. This result tree could have just the same structure, or equally the structure could be completely different. The second process is 'formatting', where one defines how the result tree should be presented (in terms of layout, fonts etc.) in a browser. The XSL specification, currently a working draft, can be found here.

XLink & XPointer

The hyperlink has been the basis of the Web's functionality. However, HTML's hyperlink is basic in comparison to the linking techniques that XML will be able to employ. These linking techniques are described in the XLink and XPointer specifications. As well as the unidirectional hyperlinks that HTML allows, XLink allows multi-directional links, links with multiple destinations, and even links that allow you to annotate read-only documents. As well as replacing your current browser display, clicking on a link might also open a new window or even embed the linked information into your current document. XPointers allow you to link to a specific part of a document without having to place 'anchors' there, simply by describing that particular point in the document's tree structure. The official XLink specification can be found here and the official XPointer specification here. Both of these specifications are currently working drafts.

Namespaces in XML

Because XML allows you to create your own tag names, two documents may use the same tag to mean different things, and this 'collision' of tag names may end up causing problems. Namespaces allow elements and attributes to have a unique form by attaching URIs to them. The official specification can be found here. It is an official World Wide Web Consortium Recommendation.

This is the end of the XML tutorial. If you wish, you can go back to the last section.

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