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XML, the eXtensible Markup Language is becoming a standard format for storing data on the web. XML is a simplified version of SGML. Wordprocessors like abiword store data as XML. Here is an example, test.abw . Unlike the limited tag-set offered by HTML, XML allows authors to define tags based upon the logical structure of their documents. It is so possible to create other languages. These are written in the form of a DTD (document type definition) or more recently with the XML Schema language. If you know TeX, LateX or HTML, XML looks quite familiar. Adapted from XML in 10 points :

  • XML is a format for structuring data. It is not a programming languague.
  • XML has tags and attributes and looks a bit like HTML but the rules are more strict.
  • XML is a text format not a binary format. The advantage is that the data can be inspected with a text editor and that it is easy for scripts to process the data.
  • XML is verbous by design and human readable. Small storage size can be achieved by compression.
  • XML is a family of technologies. It is used for example together with CSS or DOM similar than HTML. An other example is SVG, the scalable vector graphics format which or MathML, the Mathematical Markup Language.
  • XML takes the best SGML and HTML.
  • XML leads HTML to XHTML. The later has a slightly changed syntax and aims to be the successor of HTML.
  • XML is modular. Similarly as LaTeX can use different style files in parallel, XML can use different document structures simultaneously.
  • XML provides a syntax for the resource description framework (RDF), a language to express data in a relational way aiming for a "semantic web".
  • XML is licence-free, platorm-independent and well supported. Similar as LateX for mathematical typesetting or SQL for relational databases, this assures that the data will processable also in the future.
XML Tools for the Mac: (by Eric Zelman):

Simplicity, Clarity, Generality B.W. Kernighan, R. Pike, in "The Practice of Programming".