Actor Instance   An actor instance is a specific instance of an actor using the entity being modeled, which is most typically a system but could be a subsystem or a class. It has unique identity as well as attribute values, which determine its state at any point in time. An actor instance communicates with one or more instances of use cases sending message instances.

Explanation

An actor instance is a specific example or instance of an actor. Given that an actor most typically represents a role that a user (or other system) plays with respect to the system being modeled, an actor instance is a specific example of a user or system; and can be named and identified. The concept is that while an actor describes the role from a generic point of view, an actor instance describes or represents an actual or specific example of the actor. In our natural language we use this idea regularly when we say "a person" - we are not referring to a particular person. However when we say, "the person we spoke with last week", we are speaking of a specific person. This is part of what is known as the type-instance dichotomy, which occurs with many of the UML elements.

Related Entries

Actor  Used Together An actor is related to an actor instance in that an actor is the type from which the instance is derived. An actor represents a generic role the user (or another system) plays, whereas the actor instance is a specific example of a user or another system.