The message model provides some facilities that are not specified in the XML Schema 1.0 specification.
A message is a global element that represents an entire message (rather than a structure within a message). Within a message definition file, a message is represented by a special global element that carries the extra information required by WebSphere® Message Broker.
The message model adds the following compositions that are beyond the XML Schema 1.0 specification:
Compositions orderedSet and unorderedSet allow message models that were produced in earlier versions of the product to be supported.
If one or more physical formats are defined for a message set, the XML Schema objects within the message set can hold extra information about how they should be parsed and serialized.
For details about XML Schema, see XML Schema Part 0: Primer on the World Wide Web Consortium (W3C) Web site.