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And that's exactly what we're going to look at next,
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relationships in the class diagram, how they're represented and
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what they mean. First of all relationships as the
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name says, describe interactions between classes or between objects in
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my system. And we will describe three main types
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of relationships. The first one is called a Dependency
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relationship. And we can express that as X uses
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Y and we represent it with a dashed directed line.
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So when we have such a line between two classes
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that means that the first class uses the second one. And
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we're going to provide an example of a dependency in a
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minute. The second type of relationship is an association that can
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also be an aggregation. We'll see what the distinction is.
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But basically, what this means is that we can express that
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as a X has a y. So x contains a
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y. And if it is in association, we indicate it with
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a solid undirected line. If it's an aggregation,
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we indicate it in the same way, but with
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a diamond at one of the ends. Finally, the
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third type of relationship is what is called Generalization.
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And this can be expressed as x is a
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y. So this is the relationship that expresses inheritance.
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Specialization between two classes. It's represented with a solid
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directed line with a large open arrow head at
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the end. Going from the more specialized class to
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the less specialized class. So going from the subclass to
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the super class. So now let's look at each relationship
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in more detail using our example, our course management system.
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