Message Sets: Message definition files
A message definition file contains the messages, elements, types, and groups which make up a message model within a message set.
Every message set requires at least one message definition file to describe its messages. Message definition files use the XML Schema language to describe the logical format of one or more messages. Extra information in the form of XML Schema annotations is used to describe any physical formats that you define for the messages.
Large message sets can contain several message definition files. This keeps the individual files to a manageable size, making them faster and easier to work with.
Message definition files can be created by using the Message Definition editor, or can be imported from a range of different file formats as described in Importing from other model representations to create message definitions.
A message definition file can be associated with a namespace, so that all message model objects that are declared within the file belong to that namespace. Namespaces provide a means of avoiding name clashes among similarly named global objects. They are described in detail in Namespaces in the message model.
One message definition file can reuse message model objects that are defined in another message definition file. XML Schema provides two mechanisms to do this: import and include. For more information, see Reusing message model files.