Which statement best describes an event in a state machine diagram?

• A. A type of occurrence that can trigger a behavior within an operational system
• B. A variable used to store data during execution
• C. A component that executes operations
• D. A diagram that shows state changes

Answer: (A)

An event in a state machine diagram is an occurrence that can trigger a behavior or a transition in the system. It’s something that happens externally or internally (like a user action, a signal, or a timer) that causes the system to move from one state to another or start an activity. This is why the statement that an event is a type of occurrence that can trigger a behavior within an operational system best describes it.

Think of it this way: if a user presses a button, that press is an event. It doesn’t hold data or perform work itself; it prompts the system to change state or execute an action. By contrast, a variable stores data, a component executes operations, and the diagram itself is the overall representation of states and transitions, not a single event.