Chapter 10. Communicating Objects

In Executable UML, we build statechart diagrams and state transition tables for classes and associations to capture their lifecycle behavior. The behavior is defined in actions, grouped together as procedures on the state machines. The behavior is sequenced by signals between state machine instances.

By formalizing behavior as actions in procedures, we make the procedures, the state machines, and so the entire domain model, executable.

Each procedure on a state machine is written using an action language such as that introduced in Chapter 7: Class Actions. This chapter extends these actions to include signaling to existing objects and signaling to cause creation of other objects. Certain rules govern the construction and receipt of the signals and their parameters to maintain consistency of the actions.

For completeness, this chapter describes also the synchronous creation and deletion of objects that have state machines.

Collaboration diagrams help visualize the communication patterns between the several classes, and sequence diagrams illuminate the execution of a single scenario, with known states and attribute values, over time. In this chapter, we show how to use these diagrams, known collectively as interaction diagrams, to understand patterns of communication between existing state machine instances and external entities.