When a system should be included as an actor in use case diagram?

Question

Hi.
I'm making a use case diagram for a new system. I'm wondering when a system should be included as an actor in use case diagram?

Thanks.

Answer 1

Different people have different philosophies about how to correctly model in UML (which is not surprising since UML was standardized by committee).

I use actors to capture every "thing" (type of person, type of system) that can interact with the system I am designing and find them useful to create a common understanding among all stakeholders of how the new system will be interacted with.

I suggest creating an actor for everything you know will interact with the system, and trace that actor to every use case the actor can execute. That way, you gain a full understanding of who can do what.

Answer 2

Actor as stated in another answer is system or role interacting with system under development. You should include a system into use case as an actor, if that system is outside of the system you are developing and if it directly interacts with that system you are developing.

This is important because you need to define boundary of your system, which means its scope and interfaces. Including system as an actor will clearly state requirement for your system under development to provide suitable interface for that actor system.

Answer 3

This topic might also help clarify when to represent systems as actors: UML Use Case Diagrams: Reference