Now, let's look at use cases in a little more detail.
And start by defining exactly what an actor is. An actor
represents an entity, which can be a human or a device,
that plays a role within my system, so that interacts with my
system. It's some entity from the outside world, with respect to
my system, that interacts with my system. It is important to
clarify that an entity can play more than one role. For
example, you might have somebody working in a bank that can be
both an employee of the bank, or a customer of
the bank, depending on how it interacts with the banking
system. And, obviously, more than one entity can play the
same role. Using the same example, we can have both an
employee of the bank and just a regular customer, playing
the role of the customer. So again, it all depends on
what the entity does, how the entity interacts with the
system, what kind of functionality of the system the entity uses.
And finally, actors may appear in more than one use case.
So it's fairly normal for the same actor to interact with
the system in different ways. And therefore, to appear in more
than one use case. Just think about the use cases in
scenarios of usage. If the same actor can interact with the
system in different ways, that actor will appear in multiple use
cases. Now let's go back to the description of our course
management system, and see how we can identify actors in the system.
And as we did for the class diagram before, I encourage
you to stop the video and try to identify the actors
in the system yourself, before I do it.
If we look at the description, we can see that, for example, the Registration
Manager is clearly an actor for the system. Students are actors
for the system. Professors are actors for the system. And notice
that we're not doing the same thing that we were doing
when identifying classes. Here we're identifying
entities that are from the outside
world, and have an active role in interacting with my
system. Again, Registration Manager, that we will just call registrar for
simplicity, students, and professors. So once we have identified the
actors for our example, we can simply draw them, using the
notation that we just introduced. So we have the registrar,
and notice how for every actor we clarify the role that
the actor plays. We have the professor, and we have
the student. So here, these are the three actors that we
identified for our system.