Object-Oriented Modeling and Design with UML (2nd Edition) — B.Tech Lecture Notes[cite: 1]
An event is an instantaneous occurrence that can trigger a state transition[cite: 1]. UML categorizes them into three distinct primary types[cite: 1]:
An explicit, asynchronous message sent from one object to another[cite: 1].
Example: Pressing a power button on a TV remote[cite: 1].
Figure 5.1: Signal Event Transition Diagram
Fired continuously monitoring a boolean condition; triggers automatically when condition evaluates to true[cite: 1]. Syntactically noted using when (condition)[cite: 1].
Example: A thermal sensor activating a cooler when room temperature exceeds 30°C[cite: 1].
Figure 5.2: Change Event Transition Diagram
Triggers after the passage of a specified duration or reaching a specific clock time[cite: 1]. Syntactically noted using after (duration) or at (time)[cite: 1].
Example: A web application timing out an inactive user session after 5 minutes.
Figure 5.3: Time Event Transition Diagram
Combining various event types into a cohesive multi-mode system model:
Figure 5.4: State Diagram using multiple Event Types
Signal: direct event name e.g., cardInserted()[cite: 1]Change: starts with when e.g., when(fuel < 5%)[cite: 1]Time: starts with after or at e.g., after(30 sec)[cite: 1]