Relationships

Relationships in the UML:  There are four kinds of relationships in the UML:

1.      Dependency

2.      Association

3.      Generalization

4.      Realization

Dependency is a semantic relationship between two things in which a change to one thing  may affect the semantics of the other thing

                        Graphically a dependency is rendered as a dashed line, possibly directed, and occasionally including a label

 

Association is a structural relationship that describes a set of links, a link being a connection among objects.

Graphically an association is rendered as a solid line, possibly directed, occasionally including a label, and often containing other adornments, such as multiplicity and role names

Aggregation is a special kind of association, representing a structural relationship between a whole and its parts. Graphically, a generalization relationship is rendered as a solid line with a hollow arrowhead pointing to the parent.

Realization is a semantic relationship between classifiers, wherein one classifier specifies a contract that another classifier guarantees to carry out. Graphically a realization relationship is rendered as a cross between a generalization and a dependency relationship.