This blog post discusses the role of primary and secondary actors in UML use cases. Primary Actors are actor(s) using the system to achieve a goal. The Use Case documents the interactions between the system and the actors to achieve the goal of the primary actor. Secondary Actors are actors that the system needs assistance from to achieve the primary actor’s goal. Additional references about Primary and Secondary Use Case Actors
Guideline: Find and Outline Actors and Use Cases
Identifying Actors in Use Case Diagrams
Types of Actor in a Use Case Model
What is the difference between a Primary and Secondary Actor in Use Case Modeling?