UML - Association, Aggregation, Composition, Generalization, Specialization, Realization and Dependency

Association

Association is a simple relationship between two classes.

For example

A relationship between Professor Class and Student class is known as Association.

Both Classes can exist without each other, so Professor and Student are two independent classes. In this kind of relationships there will not be any owner class. Both classes have their own life cycle.

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Aggregation

Aggregation is a special type of Association. It is known as “Has-A” relationship.

For example

A Department class can contain Professor Class. Here Department class is owner class. Here in this relationship even after deleting Department class, Professor Class can exits.

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Composition

Composition is a special type of Aggregation. It is known as “Is-A” relationship.

For example

A University Class has many Department class. Here University and Department objects are dependent on each other. If we delete University class then Department class don’t exits. Here University class is an owner class.

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Generalization

Generalization is the process of extracting shared characteristics from two or more classes, and combining them into a generalized superclass. Shared characteristics can be attributes, associations, or methods.

Generalization is a relationship between a Parent and its Derived class. It is nothing but inheritance.

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Specialization

Specialization means creating new subclasses from an existing class. If it turns out that certain attributes, associations, or methods only apply to some of the objects of the class, a subclass can be created.

Realization

Realization is a relationship between the blueprint class (Interface) and a class containing its respective implementation details.

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Dependency

Change in structure of a class affects other classes then there is a dependency between those classes.

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