Actor

How to read it

UML 2.5.1 defines an actor as a type of role played by an entity that interacts with the subject of its use cases, usually the system being described, and says actors may represent roles played by human users, external hardware or other systems. The figure stands for a role, not a particular person: the specification notes that one person can play several actors, and one actor can be played by many people. The actor's name is written near the figure, usually above or below it. A solid line joins the actor to each use case it takes part in. Scott Ambler, in The Object Primer, describes actors as drawn on the outside edges of the diagram, each involved in at least one use case.

Also searched as: actor symbol, stick figure uml, uml actor, use case actor.

Other ways to draw an actor

The specification also allows an actor to be drawn as a class rectangle with the keyword «actor», or as another icon, such as a separate icon for actors that aren't human. A billing system or a card reader may therefore appear as a box marked «actor» rather than a stick figure.

Arrowheads and primary actors

Some diagrams put an arrowhead on the line between an actor and a use case. Ambler says it is often used to show who starts the interaction, or which is the primary actor, and that the line doesn't mean information flows one way; he leaves arrowheads off because readers take them for data flow. King Saud University's course notes define the primary actor as the one who starts a use case and a secondary actor as one needed to complete it.

Look-alikes

A stick figure at the top of a sequence diagram is the same actor taking part in one interaction, with a Lifeline below it.