Actor-Use case Association   An actor-use case association is a semantic relationship between an actor and a use case. This association is typically not named and consists of exactly two association ends. The association ends are simply the end parts of the association where they connect to the actor at one end and the use case at the other. It is the association's ends that may have a number of adornments that express the rich structural semantics of the relationship.

Explanation

An association between an actor and a use case represents a semantic relationship between the actor and the use case. The actor interacts with the subject by passing messages to and from the use case. The association between the actor and the use case is the only way an actor can communicate with the subject (typically a system) that is being represented by the use case. This type of association has significantly different semantics from other examples of the association such as an association between two classes. Aggregation is not used, and navigability typically represents whether an actor can initiate a use case or not.

Important Points

		Actors cannot have associations with other actors.		Even though people or systems play the "role" of a particular actor and people (and systems) clearly communicate with each other, the UML does not allow actors to have associations with each other. The only relationship that can exist between two or actors is the generalization relationship. This does not mean that communication between the two individuals does not exist in the real world. It simply means that when modeling the system or entity it is outside the scope of interest.
		An individual actor may be associated with more than one use case.		Actors can be associated with one or more use cases, and an individual use case may be associated with a number of different actors.
		An individual use case may be associated with more than one actor.		An individual use case may be associated with a number of different actors. The significance of this is that even though a single actor may initiate the use case a number of other actors may be affected by the use case.
		The association between an actor and a use case can involve at most one actor and one use case.		Actors and use cases are both classifiers, but even though other classifiers can participate in n-ary associations, actors and use cases cannot. The association between an actor and a use case can only involve a single actor and use case. This is known as a binary association. This does not mean that a use case cannot be associated with many actors or an actor be associated with many use cases. It simply means that a separate association must be used. It also does not restrict the use of multiplicity in the association.

Related Entries

Actor  Used Together An actor is related to an actor-use case association in that an actor is one of the two participants in the association, the association connecting at the other end to a use case. The actor-use case association describes a semantic relationship between the actor and the use case implying that the actor gets some observable value from the subject described by the use case.

Use Case  Used Together A use case is related to an actor-use case association in that a use case is one of the two participants in the association, the association connecting at the other end to an actor. The actor-use case association describes a semantic relationship between the use case and the actor implying that the use case delivers some observable value to the actor that uses the subject to achieve some discreet goal.