Logical Data Modeling - Aggregation (Collection)


aggregation is a containment relationship where one or more entities are part of a container entity.

In other word, aggregation is combining multiple pieces of data into one unit.

The container entity may be:

aggregation is also known as:

  • whole/part relationship
  • catalog containment because when the container is destroyed, the content object is not destroyed (whereas in a composition it is).

In other term, this is not a dependency relationship (whereas a composition is)

The container is said to be an aggregate/compound type.

The structure to implements this kind of relationship is known as a collection.


  • Library and Students. Because the student can exist without library, the relation between student and library is aggregation.
  • professor and students: when the professor dies the students do not die along with him or her.


A aggregation is:


In a Object - Class Diagram (UML), an aggregation is represented with an association (ie the link) with a hollow diamond at the aggregate end.

Magical Number Seven, Plus or Minus Two


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