Definitions: Events, States, and Transitions - UML

An event is a significant or noteworthy occurrence. For example:

  • A telephone receiver is taken off the hook

A state is the condition of an object at a moment in time the time between events. For example:

  • A telephone is in the state of being "idle" after the receiver is placed on the hook and until it is taken off the hook.

A transition is a relationship between two states that indicates that when an event occurs, the object moves from the prior state to the subsequent state. For example:

  • When the event "off hook" occurs, transition the telephone from the "idle" to "active" state.

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