Now that we’ve identified possible collaborations between the objects in our ATM system, let’s graphically model these interactions using the UML. Several types of interaction diagrams model the behavior of a system by showing how objects interact with one another. The communication diagram emphasizes which objects participate in collaborations. [Note: Communication diagrams were called collaboration diagrams in earlier versions of the UML.] Like the communication diagram, the sequence diagram shows collaborations among objects, but it emphasizes when messages are sent between objects over time.