A communication diagram shows the dynamic
collaboration between elements. It is similar to the sequence
diagram and the intention is to focus on how the objects
collaborate with each other. Communication diagrams show the
exchange of messages (or interactions) between objects as well as
the relationships (often called context).
Often a choice will be made to use either the
sequence or the communication diagram. If showing the time or
sequence of events is most important, the sequence diagram should
be used. If showing context is most important the collaboration
diagram should be used.
The communication diagram is drawn as an object
diagram, where a number of objects are shown along with the
relationships between them. Message arrows are drawn between then
to show the flow of messages between the objects. Labels are placed
on the messages that show the order within which the messages are
sent.
Example:
Example using stereotypes:
