ITPEC FE Subject A April 2026 Question 35

Use case diagram — shows the actors, the functions they need, and how those functions relate.

It is the UML behaviour diagram used at requirements time: stick-figure actors on the outside, ovals for use cases inside the system boundary, with include and extend relationships between them.

Answer (d)

Why not others:
- (a) Activity diagram — models the flow of steps within one process; it shows control flow, not the catalogue of system functions
- (b) Communication diagram — shows objects exchanging messages in one scenario, an interaction rather than an overview
- (c) Interaction overview diagram — stitches interaction fragments into a control flow; it summarises interactions, not actors and their functions

Key rule: Use case diagrams answer "who uses the system and what for". Any diagram describing the ordering of steps or the exchange of messages is modelling how a function works, not which functions exist.

AI-generated — may contain errors