A state models a situation during which some (usually implicit) invariant condition holds. The invariant may represent a static situation such as an object waiting for some external event to occur. However, it can also model dynamic conditions such as the process of performing some activity (for example, the model element under consideration enters the state when the activity commences and leaves it as soon as the activity is completed).
Entry and exit actions are executed when entering or leaving a state, respectively.
You can create these actions in statechart diagrams as special nodes, or as stereotyped internal transitions.
Create a composite state by nesting one or more levels of states within one state. You can also place start/end states and a history state inside of a state, and draw transitions among the contained substates.
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