When we wish to reason about events, however, we can model them as objects. For a given time granularity, a transition may be considered to be instantaneous and atomic. However, transitions may be decomposed into other states and transitions in a finer granularity. Several general comments made during the workshop about behavior are worth preserving. It is useful to model states and state transitions, and then treat the stimuli for the transitions as candidate stimuli for invoking services.
Threads of execution are prime movers for computation.
Concurrent behavior consists of multiple threads of execution either happening simultaneously or appearing to happen simultaneously. When several objects each have a thread of execution, the system exhibits inter-object concurrency. If an object contains multiple threads, it exhibits intra-object concurrency. Flow of behavior is separate from flow of control even if flow of behavior is implemented with flow of control. In passive object models, a thread follows a computational activity from object to object.