16.3 Collaborations between Subsystems

Similarly, when a class has state behavior, there are collaborations between classes in different subsystems.

When a class in one subsystem collaborates with a class in another subsystem, we show the imported class on the collaboration diagram using only the name of the class, with either an annotation "from <subsystem name>," or a stereotype «imported», as shown in Figure 16.5.

Figure 16.5. Imported Classes on a Collaboration Diagram

The external entities (e.g., Customer, Warehouse Supervisor) are not part of any subsystem. They represent the explicit interface points to the domain.

To depict the collaborations between subsystems, show directional dependencies with the names of the signals, as illustrated in Figure 16.6.

Figure 16.6. A Package Diagram Showing Spanning Collaborations Between Subsystems