Difference between Composition and Aggregation.



Difference between Composition and Aggregation...

Answer / amit parashar

Composition : Defines a strong-coupled relationship between
two entities, where the one entity is part of another, and
both need each other for their existence. e.g. Human body
and the Heart.

Aggregation : Defines a weak-coupled relationship between
two entities, where one entity could be part of another, but
either can exist without the other, independantly. e.g.
School and teacher.

"Aggregation differs from ordinary composition in that it
does not imply ownership. In composition, when the owning
object is destroyed, so are the contained objects. In
aggregation, this is not necessarily true. For example, a
university owns various departments (e.g., chemistry), and
each department has a number of professors. If the
university closes, the departments will no longer exist,
but the professors in those departments will continue to
exist. Therefore, a University can be seen as a composition
of departments, whereas departments have an aggregation of
professors. In addition, a Professor could work in more
than one department, but a department could not be part of
more than one university."

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