Multipart messaging occurs when you embed a message within another message.
Multipart messages are useful when a message has a format as shown below. The Message Header and Message Trailer act as an envelope for the message body. They have a fixed format, but the Message Body can be defined with different formats.
A place holder for a message is created by setting the Group composition property of a type to Message. This forces the separation type to become undefined for this type and allows a message to be added at this point within the first message, creating a multipart, or embedded message. Such an embedded message must be specified earlier in the outer message by use of a Message Key.
Each type or group with composition Message must be preceded in the model by a string element whose Interpret Element Value property is set to Message Key. Also, each message that is to be used as an embedded message must have its Message Key value set.
When a message is input to a flow, a string element which has been designated as a Message Key should have a value which corresponds to the Message Key of the next embedded message in the bit stream.