Use case diagram: actor with more permissions

Question

Regarding Use-Case Diagram: Consider 2 kinds of actors: Customer & User. Customer is a User (generalization) I want to model the use case of a Search option for items ('search items') which is allowed for all users without the need for a login : but only a customer (because he is registered) could take part in the use case add items . note that this means that the customer will also need to be logged in for this to happen. I can't seem to make it work without messing up the whole diagram. Thanks!

Answer 1

Simply add a constraint to the use case. You can make that visible in a diagram by using a constraint element which looks like a note but has the text enclosed in curly brackets.

Answer 2

As is noted in the specs :

NOTE. An Actor does not necessarily represent a specific physical entity but instead a particular role of some entity that is relevant to the specification of its associated UseCases. Thus, a single physical instance may play the role of several different Actors and, conversely, a given Actor may be played by multiple different instances.

Thus there is no reason to try to mash multiple use cases into single Actor; User and Customer represents two different roles and thus it is often better to represent it by two actors; the fact that Customer is derivation of User can represented by a generalization.

And finally you can add a note to the use-case association to specify that the Customer has to be logged in - but at least for me this seems unnecessary, because the User already had to log in in order to take on the "Customer" role.