Association Class   An association class has the behavior of both an association and a class. It gives an association the ability to have attributes and operations like a class. It has two distinct parts to its structure: an association part and a class part.

Explanation

An association class is both an association and a class that allows the addition of attributes and operations that describe the association. It describes additional information about the association that can't be expressed in the classifiers at the end of the association. It should not be confused with a many-to-many relationship, which has quite a different meaning connecting three or more classifiers that all have a relationship with each other.

Important Points

An association class may be attached to an n-ary association.

When used with an n-ary association it has the same semantics, but its appearance is a little different. In this circumstance the association part of the association class is replaced by the diamond of the n-ary association, the association class is recognizable from the other classifiers because it is attached to the diamond by a dotted line.

Related Entries

N-ary Association  Confused with,  Graphically Similar An n-ary association is related to an association class because it is often confused with an association class. The two elements have very different semantics. The association class adds attributes and operations to the relationship, but it does not itself participate in the relationship. An association class connecting two classifiers can be confused with an n-ary association between three classifiers. They have a similar graphical appearance - there are lines connecting three classifiers. In the case of the n-ary association all three classifiers participate in the relationship and each classifier has a distinct relationship with the other two classifiers.

Association  More General An association is related to an association class because it represents the association part of the association class. The association class has, in addition to being a class the additional property of adding a relationship between the two classifiers it is connected to.

Class  More General A class is related to an association class because it represents the class part of the association class. The association class has, in addition to being an association, the additional property of adding class attributes and operations.