Use case diagram
The notation of the UML use case diagram: primary and secondary actors, use cases, the system boundary, include, extend and generalisation relationships.
- 21 cards
- 4 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- Concepts
- Questions
- Sort and link
- Understand
A few cards from the deck
Primary actor: what is it?
Show the answer
A role outside the software that starts a use case to reach a goal.
It is a role, not a person: one user can play several roles (customer, administrator), and another piece of software can play one.
A booking application calls a bank service to validate a card. What is that service's role in the diagram?
- A secondary actor, called on by the software
- A primary actor, because it takes part in the use case
- A use case, because it provides a service
- A subsystem, drawn inside the boundary
Show the answer
A secondary actor, called on by the software
The service is outside the software and starts nothing: it answers. It is therefore an actor, and a secondary one. Taking part in a case is not enough to be primary: it has to start it.
A use case's name starts with a …: “Buy a ticket”, not “Ticket” nor “Click Submit”.
Show the answer
A use case's name starts with a verb: “Buy a ticket”, not “Ticket” nor “Click Submit”.
A noun alone does not say what the actor gets, and a click describes the screen, not the goal.
Secondary actor: what is it?
Show the answer
A role outside the software that it calls on to complete a use case, without having started it: a bank, a payment service.
To tell it from the primary one, look at who takes the initiative: the primary actor starts the case, the secondary one answers the software.
Why is “Click Submit” not a use case?
- Because a use case's name must never start with a verb
- Because only secondary actors act on the screen
- Because a use case must always be joined to at least two actors
- Because it is a screen gesture, not a complete goal of the actor
Show the answer
Because it is a screen gesture, not a complete goal of the actor
The diagram says which services the software provides, not how the screen is built. Clicking Submit is a step described later, inside the flow of a case like “Buy a ticket”.