Actors are the users of the system being modeled. Each Actor will have a well-defined role, and in the context of that role have useful interactions with the system.<br /></p><p><br /></p><p>A person may perform the role of more than one Actor, although they will only assume one role during one use case interaction.<br /></p><p><br /></p><p>An Actor role may be performed by a non-human system, such as another computer program.<br /></p>