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Unified Modeling Language Reference Manual, The, Second Edition by Grady Booch, Ivar Jacobson, James Rumbaugh

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aggregation

A form of association that specifies a whole-part relationship between an aggregate (a whole) and a constituent part. It is also applicable to attributes and parameters.

See also composition.

Semantics

A binary association may be declared an aggregation—that is, a whole-part relationship. One end of the association is designated the aggregate while the other end is unmarked. Both ends may not be aggregates (or composites), but both ends can be unmarked (in which case, it is not an aggregation).

The links instantiated from aggregation associations obey certain rules. The aggregation relationship is transitive and antisymmetric across all aggregation links, even across those from different aggregation associations. Transitivity means ...

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