8.3. Referential Constraints
When we begin abstracting classes and attributes, our candidate classes might include attributes such as
Book.publisher
CreditCardCharge.accountNumber
Order.customerID
Attributes like these are characteristics of the classes, but they also refer to the related classes. It is important, then, that we capture the fact that each such attribute is tied to an association.
8.3.1. Referential Attributes
A referential attribute identifies the instance of the associated class.
Definition: A referential attribute is an attribute whose value is the value of an identifying attribute in one or more associated classes.
We tag the referential attribute with {Rn}, where n is the number of the association being formalized. For example, ...
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