Definition:
Shared aggregation (aggregation) is a binary association between a property and one or more composite objects which group together a set of instances. It is a “weak” form of aggregation when part instance is independent of the composite. Shared aggregation has the following characteristics:
- it is binary association,
- it is asymmetric – only one end of association can be an aggregation,
- it is transitive – aggregation links should form a directed, acyclic graph, so that no composite instance could be indirect part of itself,
- shared part could be included in several composites, and if some or all of the composites are deleted, shared part may still exist.
Further Reading:
Book: The Unified Modeling Language Reference Manual by James Rumbaugh, Ivar Jacobson and Grady Booch.