Use Case Diagram - two actors to one use case

Question

I want a use case - store information system. I am to present the owner's requirements on a use case diagram, incl. a customer who, after logging in, does shopping, and an admin, who after logging in, manages prices, etc.

Can I log into the system generalize from one use case - two actors combined with one use case (below)? How can I 'improve' the diagram?

Answer 1

UML does not specify the semantic when more than one actor is associated to the same use-case. It can mean for example that one of the actors only is involved without the other, that the two actors are involved at the same time, or that the two actors are involved one after the other.

For sure, actors and use-cases are classifiers. You can therefore use generalization of use-cases or of actors (as explained with an example here) .

But your diagram, while syntactically correct, has some issue:

• First Admin account is not a use-case: it does not produce any observable results to the actor; it is an internal detail of the sytem. So it does not correspond to the UML criteria of a use-case.
• Then, Login, Confirm password (and perhaps Checkout?) do not correspond to user goals. As explained here, this is not fundamentally wrong according to the UML specifications, but it is a bad practice. Use-cases are meant to describe actor goals, and not details of a process or a user interface.
• Maybe i'm old school, but you should also surround the use-cases with a box representing the "subject", i.e. the system under consideration.

Answer 2

There's no special magic about it, UML Use Case describes a case and can have more than one user.

Maybe just moving the shared Use Cases next.

But, since Use Case diagrams support User Inheritance as if they were classes, maybe adding a generic abstract superclass alike GenericUser with the shared Use Cases, and subclass alike User and Admin with their own specific Use Cases would be useful.