What Is XML?

By Steve Hoenisch
Last updated on May 25, 2002 | Search this page: Ctrl+F
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Related Documents
 An Introduction to XML
 Structuring Documents in XML
 Developing a Document Type Definition
 Attributes and Entities in DTDs
 An Introduction to XSL
 Using XSLT to Separate Content from Presentation
 XML Linking: An Introduction
 XML in 10 Points
 a technical introduction to XML
 Converting Unstructured Documents to XML

Extensible Markup Language is a metalanguage for describing and structuring data with tags. Metalanguage means a language for how to describe other languages. Like HTML, XML uses tags (words bracketed by "<" and ">"), but unlike HTML, XML has neither a predefined set of tags nor rules for how to use them (though XML does have generic rules governing markup; for instance, tags may not overlap). In XML, tags and the rules for them, or grammar, are defined by the users themselves.
XML programmers use tags and their corresponding grammar to describe and structure data in text files (as opposed to a binary format), making the data easy to reuse, manipulate, and search. Because users can define their own tags, XML, as its full name implies, is also extensible, meaning that, unlike HTML, it is capable of being extended.
The hodgepodge of abbreviations and acronyms surrounding XML points up another of its characteristics: It is a family of technologies designed to be used over the Internet. Some of XML's family members and their main functions are as follows:
You can visit the World Wide Web Consortium's (W3C) web site, http://www.w3c.org, for the rundown on most of these initiatives.
For another description of what XML is and what its core related technologies are, take a look at "XML in 10 Points," at http://www.w3.org/XML/1999/XML-in-10-points.
For a technical introduction to XML, visit http://www.xml.com/pub/a/98/10/guide0.html.
An article called "Converting Unstructured Documents to XML," at http://xml.oreilly.com/news/xmlnut3_0301.html, demonstrates how to isolate atomic elements to reveal a document's underlying structure and convert it to XML.
The tutorials in this series proceed as follows:
  1. An Introduction to XML
  2. Structuring Documents in XML
  3. Developing a Document Type Definition
  4. Attributes and Entities in DTDs
  5. An Introduction to XSL
  6. Using XSLT to Separate Content from Presentation