ITPEC FE Subject A April 2024 Question 34

State and Transition — a UML state machine diagram shows the states an object passes through and the transitions between them.

A state (rounded rectangle) is a condition in which the object waits or acts; a transition (arrow) moves it to another state when an event occurs, optionally under a guard condition and with an action. Initial and final pseudostates mark where the life cycle starts and ends.

Answer (d)

Why not others:

• •(a) Message and Activity — messages are exchanged between objects in sequence and communication diagrams; activities (actions and control flow) are the elements of an activity diagram
• •(b) Message and Transition — transition belongs, but message is a sequence or communication diagram element
• •(c) State and Message — state belongs, but message is again a sequence or communication diagram element

Key rule: Name each UML behavior diagram by its building blocks: states and transitions (state machine), actions and control flows (activity), lifelines and messages (sequence).

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