The primary goal of this model is to articulate to the reader the context in which the domain sits.
It shows roles, organisations, systems (software) and hardware components as actors
From the “use case context view” the reader can get a sense of those things that will interact with the system that is being modelled without concerning themselves with the detail of the system at this point in the development cycle.
The actors represent those things that interact with the system as source and/or sinks of information and messages to the system. The system can not exercise any control over the actor, it may request or transmit information to the actor, but the actor is under no obligation to communicate with the system.
Let’s see this at work...
We have placed a question mark under the actor drawn on the left because we want to establish who is the actor in this model, the “librarian” or the “card holder” for the use case “borrow book”?