UML用例图的参与者数量

Question

Is it possible for a use case to have more than one actor? And if it is, do you know of a good reference where I can find that information (book, webpage) because I am having a problem with a diagram I made for a test. Thanks.

Answer 1

Yes, a use case can have associations to multiple actors

The only true source for this information is the UML specification on uml.org

From UML 2.5 beta2 -> 18.2 Classifier Descriptions -> Actor -> Constraints

• associations

An Actor can only have Associations to UseCases, Components, and Classes. Furthermore these Associations must be binary.

 inv: Association.allInstances()->forAll( a | a.memberEnd->collect(type)->includes(self) implies ( a.memberEnd->size() = 2 and let actorEnd : Property = a.memberEnd->any(type = self) in actorEnd.opposite.class.oclIsKindOf(UseCase) or ( actorEnd.opposite.class.oclIsKindOf(Class) and not actorEnd.opposite.class.oclIsKindOf(Behavior)) ) ) 

There are no constraints relative to the relation to the actor on the side of the use case

Answer 2

Although the UML spec allows to use multiple actors an despite the fact that I have used primary and secondary actor(s) in use cases in the past I have come to the conclusion that a use case shall have only a single actor. When you go down to that paradigm you will find that the use case cut is much easier and clearer than when using multiple actors. Please see the following slides that explain this in more detail: http://de.slideshare.net/putchavn/usecase-case-is-a-dialog-not-a-process