Collaboration diagram
Collaboration Diagrams specify the interactions between two or more processes.
A Collaboration generally consists of two or more pools which represent the participants in the collaboration. Message exchanges between participants are shown by Message Flows that connect the two pools, or the objects within the pools. Pools may also be empty, in this case they are black boxes.
All combinations of Pools, Processes, and a Choreography are allowed in a Collaboration diagram.
