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Visual Modeling with Rational Rose 2002 and UML by Terry Quatrani

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Association or Aggregation?

If two classes are tightly bound by a whole-part relationship, the relationship is typically an aggregation. “The decision to use aggregation is a matter of judgment and is often arbitrary. Often it is not obvious if an association should be modeled as an aggregation. If you exercise careful judgment and are consistent, the imprecise distinction between aggregation and ordinary association does not cause problems in practice.”[1]

[1] Rumbaugh, James et al. Object-Oriented Modeling and Design. Upper Saddle River, NJ: Prentice Hall, 1991, p. 58.

Whether a relationship is an association or an aggregation is often domain dependent. What type of relationship should be used to model a car with its tires? If the application ...

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