Figure 4-1 shows a simple class model that would not surprise anyone who has worked with order processing. I'll describe each of the pieces and talk about how you would interpret them from the various perspectives.

I'll begin with the associations. Associations represent relationships between instances of classes (a person works for a company; a company has a number of offices).

From the conceptual perspective, associations represent conceptual relationships between classes. The diagram indicates that an Order has to come from a single Customer and that a Customer may make several Orders over time. Each of these Orders has several Order Lines, each of which refers to a single Product.

Each association has two association ends; each ...

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