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N-Ary Association

n-ary Association diamond used to construct non-binary associations.

Description

An n-Ary Association element is used to model complex relationships between three or more elements, typically in a Class diagram. It is not a commonly-employed device, but can be used to good effect where there is a dependant relationship between several elements. It is generally used with the Association connector, but the relationships can include other types of connector.

UML Class diagram showing a 3-way n-ary Association.

In this example there is a relationship between a Company, an Employee and a Salary.

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n-ary Association element

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OMG UML Specification:

The OMG Unified Modeling Language specification, (v2.5.1, p.201) states:

Any Association may be drawn as a diamond (larger than a terminator on a line) with a solid line for each Association memberEnd connecting the diamond to the Classifier that is the end’s type. An Association with more than two ends can only be drawn this way.