ITPEC FE Subject A October 2024 Question 34

State machine diagram — the UML behavioral diagram showing the states one object passes through and the transitions that events trigger.

A state machine diagram is made of states (rounded rectangles) and transitions (arrows) labelled with a trigger event, an optional guard condition and an action, plus initial and final states. It describes the life cycle of a single object, for example an order moving from Received to Paid to Shipped.

Answer (c)

Why not others:

• •(a) Activity diagram — shows the flow of actions in a process or workflow, with branches and parallel flows, not how one object reacts to events
• •(b) Sequence diagram — an interaction diagram showing messages exchanged between several objects in time order
• •(d) Use case diagram — shows the functions a system offers to its actors, from the user's point of view, without modelling behavior over time

Key rule: One object + events causing state changes = state machine diagram; several objects + messages in time order = sequence diagram; a process flow = activity diagram.

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