Association

Aggregation

Composition

Association relationship is denoted using an arrow.

Aggregation relationship is denoted using a straight line with an empty arrowhead at one end.

Composition relationship is denoted using a straight line with a filled arrowhead at any one of the ends.

Association can exist between two or more classes in UML.

Aggregation is a part of an association relationship.

The composition is a part of an association relationship.

There can be one-one, one-many, many-one, and many-many association present between the association classes.

Aggregation is considered as a weak type of association.

The composition is considered as a strong type of association.

In an association relationship, one or more objects can be associated with each other.

In an aggregation relationship, objects that are associated with each other can remain in the scope of a system without each other.

In a composition relationship, objects that are associated with each other cannot remain in the scope without each other.

Objects are linked with each other.

Linked objects are not dependent upon the other object.

Objects are highly dependent upon each other.

In UML Association, deleting one element may or may not affect another associated element.

In UML Aggregation, deleting one element does not affect another associated element.

In UML Composition, deleting one element affects another associated element.