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