• Collaboration (renamed to "Communication" in UML2) diagrams are an alternative presentation of a sequence diagram.
• They tend to be more compact, but harder to read, than the equivalent sequence diagrams.
• The boxes are objects.
  • Lines connecting two boxes indicate that the objects collaborate with (send messages to) one another.
  • Use a multiplicity indicator in the box (such as *****) to indicate that all elements of an aggregation receive a message.
• The Communication diagram focus is on communication as it relates to the structure of the objects involved in a task.

• The following figure models a collaboration that references an existing collaboration called "get performances."