Actor (UML)

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UML use case diagram with two actors and several use cases.

An actor in the Unified Modeling Language (UML) "specifies a role played by a user or any other system that interacts with the subject."[1]

"An Actor models a type of role played by an entity that interacts with the subject (e.g., by exchanging signals and data), but which is external to the subject."[1]

"Actors may represent roles played by human users, external hardware, or other subjects. Note that an actor does not necessarily represent a specific physical entity but merely a particular facet (i.e., “role”) of some entity that is relevant to the specification of its associated use cases. 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."[1]

UML 2 does not permit associations between Actors.[1][2] The use of generalization/specialization relationship between actors is useful in modeling overlapping behaviours between actors and does not violate this constraint since a generalization relation is not a type of association.[3]

Actors interact with use cases.


  1. ^ a b c d "OMG Unified Modeling Language (OMG UML), Superstructure, V2.1.2, pp. 586–588". Archived from the original on 23 September 2010. Retrieved November 7, 2010. 
  2. ^ "Problems and Deficiencies of UML as a Requirements Specification, s.3.2." (PDF). Archived (PDF) from the original on 17 October 2010. Retrieved November 7, 2010. 
  3. ^ "UML 2 Specification". Retrieved July 4, 2012. 

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