An initial theoretical foundation for object-oriented systems analysis and design

ion of an object’s status, phase, mode, or situation. An object may be in several different Figure 2.3 Sample state net states at any time. For example, an order object may be in the Customer Waiting and theUnpaid state at the same time. Transitions are the means by which objects leave and enter states. A transition consists of a trigger and an optional action. Triggers, which are in the top half of transition rectangles, describe the conditions or events that cause a transition to fire. Actions, which are in the bottom half, describe what an object does when a transition fires. A transition is enabled when an object is in all states of a conjunction of prior states. Usually, this amounts to an object being in one of the prior states, since prior-state conjunctions often include only one state. An enabled transition fires when the trigger holds. After firing and performing the transition’s action an object enters all states of a conjunction of subsequent states, which often consists of just one subsequent state. Transition [1] in Figure 2.3 says that if an order object is in the Open state or