UML Class Diagram Relations

CLASS RELATIONS

Aggregation (COMPOSITION related)

Represents a has-A relation between 2 objects

Composition (COMPOSITION related)

Represents a has-A relation. But, the object being referred cannot exist without the parent.

Generalization (INHERITANCE related)

Is-A relation between 2 classes (Represented as 'Inheritance' in diagram. But called as Generalization)

Realization (INHERITANCE related)

Is-A relation between a class and an interface.

Association

1. Represents 1-1/1-Many/Many-1 relation between 2 classes. Bi-directional*
2. Represented as an arrow with role and multiplicity of the relation at the ends of the arrow.
                        

Dependency

Same as Association. But, changes made to the dependent class impact the source.

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