Aggregation

It is a special form of Association where:

• It represents Has-A relationship.
• It is a unidirectional association i.e. a one way relationship. For example, department can have students but vice versa is not possible and thus unidirectional in nature.
• In Aggregation, both the entries can survive individually which means ending one entity will not effect the other entity

Composite

Composition is a restricted form of Aggregation in which two entities are highly dependent on each other.

• It represents part-of relationship.
• In composition, both the entities are dependent on each other.
• When there is a composition between two entities, the composed object cannot exist without the other entity.