A state diagram, also known as a state machine diagram or state chart diagram, is a type of behavioral diagram in software engineering that describes the behavior of an object or a system over time. It is a graphical representation of the states, events, and transitions that occur in the system.
Typical elements:
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States: A state is a condition in which an object or system exists. Each state is represented by a rectangle with a name. For example, in a traffic light, the states are "Red", "Yellow", and "Green".
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Transitions: A transition is a change from one state to another. Transitions are represented by arrows with labels indicating the events that trigger the transition. For example, in traffic light, the "Green" state could transition to the "Yellow" state when a timer expires.
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Events: An event is something that occurs that triggers a transition. Events are represented by labels on the arrows that connect the states. For example, in the traffic light system, the event that triggers the transition from "Red" to "Green" could be the expiration of a timer.
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Actions: An action is something that occurs during a transition. Actions are represented as labels on the arrows or as actions associated with the transitions. For example, in the traffic light system, the action associated with the transition from "Green" to "Yellow" could be to turn on a warning light.
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Guards: A guard is a condition that must be true for a transition to occur. Guards are represented as Boolean expressions in square brackets. For example, in the traffic light system, the guard for the transition from "Red" to "Green" could be a condition that checks if there are no cars in the intersection.