What does a signal event represent in a state machine diagram?

What does a signal event represent in a state machine diagram?

• A. Represents the receipt of a signal instance by a target structure that's receptive to it
• B. Represents the emission of a signal to a target structure
• C. Represents a time-based trigger
• D. Represents a data value change

Answer: (A)

A signal event in a state machine diagram is the moment a signal arrives at an object that is capable of receiving it. When the signal is delivered to the target, it can trigger a transition in that object's state machine, causing actions to run and the state to change. The key idea is the reception by a receptive target, not the sending of the signal. Emitting or sending a signal is what a sender does, while the event in the diagram represents the receiver handling that signal. Time-based triggers and data value changes are different kinds of events and are modeled differently (as timer events or internal changes), not as signal receptions.

A signal event in a state machine diagram is the moment a signal arrives at an object that is capable of receiving it. When the signal is delivered to the target, it can trigger a transition in that object's state machine, causing actions to run and the state to change. The key idea is the reception by a receptive target, not the sending of the signal. Emitting or sending a signal is what a sender does, while the event in the diagram represents the receiver handling that signal. Time-based triggers and data value changes are different kinds of events and are modeled differently (as timer events or internal changes), not as signal receptions.