We now discuss UML's behavioral diagrams. Those diagrams that
have to do with the behavior, the dynamic aspects
of the system, rather than the static ones. The
first behavioral diagram I want to discuss is a very
fundamental one, the Use Case Diagram. So, let's start
by seeing what a Use Case is. A Use Case
represents two main things. First the sequence of interactions
of outside entities which is what we normally call actors
with the system that we're modelling and the second thing
is the system actions that yield an observable result of values
to the actors. And basically these two things, and nothing else
that the outside view of the system. So the view of
the system in which we look at the interaction between
this system, and the outside world. If you want to parallel, think
about designing a house. Considering how you would use the house.
And you might have seen use cases called with different names.
So for example, they're also called scenarios, scripts or user stories,
but in the context of UML, we'll call the use cases.
Now let's look at the basic notation for a use case,
which is fairly simple. We have a use case which is represented
by an oval, with a name, which is the name of
the use case. We have an actor, which is represented by
this icon and is normally identified by a role name. And
finally we have an edge which is a solid line that connects
actors and use cases and indicates that an actor
is the actor of a given use case. And just
for completeness let me note there are some additional notational
elements but now for simplicity we'll just use these ones.