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Monday, August 4, 2008

XML - Introduction


Prerequisites: You must know HTML (and preferably Javascript) before you can learn XML.


What is XML?
XML stands for EXtensible Markup Language
XML is a markup language much like HTML
XML was designed to carry data, not to display data
XML tags are not predefined. You must define your own tags
XML is designed to be self-descriptive
XML is a W3C Recommendation


The Difference Between XML and HTML
XML is not a replacement for HTML.XML and HTML were designed with different goals:
XML was designed to transport and store data, with focus on what data is.HTML was designed to display data, with focus on how data looks.
HTML is about displaying information, while XML is about carrying information.


XML Does not DO Anything
Maybe it is a little hard to understand, but XML does not DO anything. XML was created to structure, store, and transport information.

XML is used to wrap information in tags. Someone must write a piece of software to send, receive or display it.


XML is Just Plain Text
XML is nothing special. It is just plain text. Software that can handle plain text can also handle XML.
However, XML-aware applications can handle the XML tags specially. The functional meaning of the tags depends on the nature of the application.


With XML You Invent Your Own Tags
The tags in the example above (like and ) are not defined in any XML standard. These tags are "invented" by the author of the XML document.
That is because the XML language has no predefined tags.
The tags used in HTML (and the structure of HTML) are predefined. HTML documents can only use tags defined in the HTML standard (
XML allows the author to define his own tags and his own document structure.

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