6/22/08

What's the difference between aggregation and containment?

What's the difference between aggregation and containment?

Answer:
UML Question.
It was quite interesting story, because I wrote the difference in terms of COM and the interviewer meant C++. The only problem that when he drew the question, it turned out that he hardly knows terminology himself. Trust me, in terms of C++ (to be precise in terms of UML) there is NO difference between aggregation and containment. Aggregation IS containment and containment IS aggregation. There is a difference, however, between aggregation and composition. This question should sound: "What's the difference between aggregation and composition in terms of UML?". Back to answer. The difference between aggregation and composition is life term of participating objects. Aggregated object can exist without container. Composited object is managed by it's container and cannot live without it. Interviewer would probably expect that you will say that composition implemented by creating object by value and aggregation implemented by creating object by reference (or pointer), but strictly saying it's not true. The true difference is who manages the life cycle of the aggregated object.

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