The following document talks about the diferrent ways in which you can validate an XML file using XSD in your application.

http://java.sun.com/j2ee/1.4/docs/tutorial/doc/JAXPDOM8.html

An xsd file can refer to another xsd file in two ways..

• using <import> tags
• using <include> tags

The <import> tag has to be used, when an xsd wants to refer another xsd whose "targetNamespace" values is different.
The <include> tag has to be used, when the "targetNamespace" of the referred xsd is same as the "targetNamespace" of the referring xsd..
You cannot "import" an xsd whose "targetNamespace" is same as the "targeNamespace" of the referring xsd file...
Similarly, you cannot "include" an xsd whose "targetNamespace" is different from the "targetNamespace" of the referring xsd file.