Java validating xml against schema
DTD-validating parsers are most common, but some support XML Schema or RELAX NG as well.
You may also view this list in XML, DAML and OWL formats or using Spectacle.
This will help you to get the basic concepts in parsing and how does DOM API differ from SAX.
See also the Semantic Web open source tool site Sem Web
An XML Schema describes the structure of an XML document, just like a DTD.
An XML document with correct syntax is called "Well Formed".
An XML document validated against an XML Schema is both "Well Formed" and "Valid".
With XML Schema, your XML files can carry a description of its own format.