XML uses tags in text to mark up data. It is also a meta language for defining other markup languages, interchange formats, and message sets. Unlike HTML's pre-defined tags, XML provides a methodology for creating custom tags. XML allows every person or organization to build a tag library to match their needs. The markup language is created in terms of a specific problem domain. This allows for innovation, but a well-formed document must adhere to the syntax rules in the W3C (World Wide Web Consortium) XML 1.0 specification. Here is an example of well-formed XML:
<?xml version="1.0"?><memo> <to>Bill</to> <from>Melinda</from> <cc>Steve</cc> <subject>XML Code</subject> <body>The 'well-formed' code sample you wanted is attached.</body></memo>
Although XML markup can be contained in a file, it can also be sent as a data stream or a database result set. It can also be dynamically generated by one application and sent to another. More accurately, an XML document can be thought of as a 'data object.' The use of XML is not limited to text markup. It could just as easily be applied to sound markup or image markup.
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