A message is a set of data that is passed from one
application to another. A message can be modeled by a message file (also
called a message definition file) that describes the structure and
content of the message. Messages must have a structure and format that is
agreed upon by the sending and receiving applications. The service flow project
tools include a flow message editor for working with nonterminal message files
(.smxsd) and creating the interfaces used by services.