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There's two more structural diagrams that I want to
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mention before we move to the behavioral ones. The
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first one's the component diagram. A component diagram is
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a static view of components in a system and of
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their relationships. More precisely, a node in a component
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diagram represents a component where a component consists of one
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or more classes with a well-defined interface. Edges conversely
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indicate relationships between the components. You can read this relationship
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as component A uses services of component B. And notice that the
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component diagrams can be used to represent an architecture, which is
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a topic that we will cover extensively in the next mini-course.
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So let's illustrate this with an example. So, what I'm representing
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here is a component diagram for our example system, the course
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management system. And as you can see, it's slightly more complex
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than the other diagrams that we saw. But there's really no
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need to go through all the steps and all the details.
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Important thing is to point out some key aspects of
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this diagram. So the first one is that these rectangular
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nodes are the nodes in the system, so are my
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components. For example, student is a component, schedule is a component,
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and so on. And as far as edges are concerned,
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I'm representing two kinds of edges. The first kind of dashed
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edges which were part of the original uml definition and
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indicate use. So an edge, for example, between this compnent and
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this compnent indicated that the seminar management uses the
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facilities component. More recently, in UML two, a richer representation
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was introduced, which is the one that I'm also showing
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here. So if we look at this part of the
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diagram, you can see this sort of you now,
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lollipop socket representation. And in this case, what this represents,
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is that a lollipop indicates a provided interface. So an
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interface that is provided by the component. So, for example,
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this security component provides encryption capabilities. The socket,
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conversely, indicates a required interface. So, for example, in
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this case, it's saying that the facilities component
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is needing access control capabilities, which, by the way,
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is provided by the security component. So in
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a sense these sockets and lollipop indicate interfaces between
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a provider of some of functionality, and the client
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of that functionality and you can look at those
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as basically APIs. So sets of methods that
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provide a given functionality. To give you another
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example, if we look at the persistence components
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the persistence component provides, unsurprisingly, persistent services. And
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those persistent services are required by several other
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components in the system. And in turn, the persistent
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components relies on the University database component to
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provide such services. So, there's the University DB components
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provide these sort of low-level database services that are used
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by the persistence component To in turn provided services. Last thing
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I want to note is that components or relationships can be
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annotated, so, for example if we look at the seminar management
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and the student administration components you can see that they
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are annotated here to indicate that they are user inferfaces. So
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that's all I wanted to say on the component diagrams, but
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again the key piece of information is that they represent components
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in the system where a component consists of one or more classes indicate the
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interfaces that these components provide or require.
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and describe the interactions between these components.
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