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Composition

A Composition connector between two UML Class elements using Sparx Systems Enterprise Architect.

Direction:

A Composition is used to depict an element that is made up of smaller components, typically in a Class or Package diagram. A component - or part instance - can be included in a maximum of one composition at a time. If a composition is deleted, usually all of its parts are deleted with it; however, a part can be individually removed from a composition without having to delete the entire composition. Compositions are transitive, asymmetric relationships and can be recursive.

Example

UML Object diagram showing a Composition hierarchy using Sparx Systems Enterprise Architect.

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Composition connector

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OMG UML Specification:

The OMG UML specification (UML Superstructure Specification, v2.1.1, p.43) states:

Composite aggregation is a strong form of aggregation that requires a part instance be included in at most one composite at a time. If a composite is deleted, all of its parts are normally deleted with it.