Any problem in computer science can be solved with another layer of indirection.
When a WTP tool processes an XML document, it often encounters references to other documents. For example, the grammar of the document might be specified by a DTD or XML Schema (XSD). This is the case with J2EE deployment descriptors, such as
web.xml (see Example 15.1). Another common case is when one document refers to the contents of other documents. For example, Web Service Description Language (WSDL) documents refer to components defined in other WSDL and XSD documents.
Example 15.1. Listing of web.xml