Defining an XML Document
XML documents can be defined using other documents. The definition document serves as a dictionary for the XML document. The advantage of using such definition documents is that, when used in conjunction with the XML document, you can be sure that the XML document follows certain basic rules as laid out in the dictionary. This reduces the chance of processing errors in your application. Such documents also serve as a handshake between two different systems that communicate with each other using XML documents.
An XML dictionary can be described using two types of definition documents: document type definitions (DTDs) and XML schemas. In this section, we look at both methods of dictionary definition.