Actor (UML)

In the Unified Modeling Language (UML), an actor is something or someone who supplies a stimulus to the system. An actor cannot be controlled by the system and is defined as being outside the system.

An actor is often thought of as a role, rather than an actual person. A single person in the real world can be represented by several actors if they have several different roles and goals in regard to a system.

Primary Actors interact directly with a system to achieve their goals. Supporting actors may be humans or systems called in to support the Primary Actor.

Stakeholders can also be modeled as actors. They do not directly interact with the system but they are affected by the success of Primary Actor interactions.

"Active" actors initiate interactions with a system, while "passive" actors act as targets of requests or are activated by the system.