Basics of XML

About XML

XML is a "meta-language" for creating markup languages that describe structured data

Because it is a subset of SGML, XML allows "generalized markup"

It is a useful language for storing structured and semi-structured text that will be published in a variety of media

XML is extensible, which means that it describes a way of defining a set of tags and attributes

By itself, XML does not define any tags.

This means that you create your own tags, effectively creating your own markup language

CML Chemical Markup Language		MathML Mathematical Markup Language
cXML Commerce Markup Language		ebXML Electronic Business Markup Language

If done correctly, XML documents written in specialized languages can be viewed across platforms

Documents can be "self describing" since they contain all of the rules that are needed to display them

An XML document contains the rules that tell browsers and parsers how to process and display the document

These rules are collected in a Document Type Definition (DTD) that is either in the header of the document or in an external document

XML opens up new possibilities for hyperlinking

Links can be multidirectional

Links can trigger actions

Documents written in XML can use any of three style sheet languages

They can use Cascading Style Sheets (CSS), Document Style, Semantics and Specification Language (DSSSL), or Extensible Style Language (XSL)

These style languages will allow documents to be transformed from one format to another (XSL allows XML documents to be transformed into HTML)