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Aggregation Diamond Placement

publish date: 2026/06/09 19:47:11.215824 UTC

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In a UML aggregation association, the diamond shape is placed next to which class, and what does it signify?

In the center of the association line; it signifies a many-to-many relationship

Next to the part class; it signifies that the part is abstract

Next to the whole class; it signifies that the whole is composed of the parts

Next to the class with fewer instances; it signifies the minority class

Correct Answer

Next to the whole class; it signifies that the whole is composed of the parts

Explanation

The diamond is placed next to the class that represents the whole. Aggregation signifies that one object (the whole) is composed of other objects (the parts). For example, in a Patient Record aggregation, Patient Record can be the whole (diamond on its end) and Patient and Consultation are the parts. The diamond indicates 'this class is composed of the connected classes'.

Reference

Software Engineering, Ian Sommerville, 10th edition

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