In the XML world, structure is everything. An XML document without a specific, well-defined structure is just an ad-hoc set of tags. Until relatively recently, though, one language to describe those tags, Document Type Definitions or DTDs, lacked the ability to specify information about tags as holders of data. In addition, it was written using a dialect of SGML that runs completely counter to the current XML specification.
It was for these reasons that the XML Schema Definition Language, or XSD specification, was ultimately developed. Utilizing XSD, it's possible to assign to an XML document a separate schema document that describes several things:
For more informationhttp://www.stylusstudio.com/xml-schema-tutorial.html
