Messages in UML

In the UML sequence diagram, messages are illustrated with an arrow symbol, together with the name of the message and its parameters (if present). In this way, in UML a message is categorically divided into two parts:

• The name of the message specifies the event.
• The arguments of the message contain the information that is attached to the message, so that the receiver can perform the necessary activities. Control information belongs in this category as well.

We refer to the information that is exchanged as a business object, if the information:

• Is coherent
• Is structured
• Covers the requirements for a certain activity (e.g., invoice, passenger list)
• Is self-contained (no in-house reference keys, etc.)
• Outlives individual interactions

In the UML model of system integration, business objects are structured information sent as arguments in a message from a sender to a receiver.