Primary and Secondary Actors (Use Case Diagram)

Use case diagram specifies use cases and the actors that interact with the system within defined use cases. The actors can be primary or secondary, depending on their involvement.

The primary actor of a use case is the actor which specifies the user goal and usually also initiates an interaction with the use case.

The secondary actor (also called supporting actor) never initiates an interaction with the use case, and it does not trigger it in any way. The secondary actor is involved in the use case to provide a service for the system as the reaction to the use case actions.

The primary actors are usually placed on the left side of the diagram. The secondary actors are placed on the right side by the convention. (The placement is not required by the standard, only recommended for easier diagram reading.)

Primary and Secondary Actor Example

Our use case diagram example shows two actors within the editorial office system - Journalist and Translator. The Journalist is a primary actor - they can write and submit articles. The Translator is a secondary actor in our system. The actor is called by the Journalist - within the Translate resources use case. The Translator never triggers the Translate resources use case.

Primary actor and secondary actor in UML use case diagram
Primary actor and secondary actor in UML use case diagram

How to Set a Primary Actor

If you want to set a primary actor of a use case using Software Ideas Modeler, select the use case, right-click on it and choose Properties from the context menu. In the Properties dialog, switch to the Use Case tab and choose the desired actor from the Primary actor drop-down box.

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