A brief summary of UML & Rational Rose – Class Diagrams, Part IV

6. Class Diagram

 

­A class diagram is used to display some of the classes and packages of classes in your system. It gives a static picture of the pieces in the system, and of the relationships between them.

­Please remember that we usually create a class diagram in the Logical View.

  

6.1 Setting Class Visibility

 

­Public suggests that the class can be seen by all of the other classes in the system.

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Protected, Private suggests that the class can be seen in nested classes, friends, or within the same class.

 

­Package or Implementation suggests that the class can only be seen by other classes in the same package.

 

 

6.2 Class Relationships

 

 There are four types of relationships you can set up between classes:

• ­Association
• ­Dependencies
• ­Aggregation
• ­Generalization

 

Associations

­An association is a semantic connection between classes. An association allows one class to know about the public attributes and operations of other class.

­ Unidirectional & bidirectional associations exist in Rational Rose.

Dependencies

 

­A dependency relationship shows that a class references another class. A change in the referenced class specification may impact the using class.



Aggregations

­An aggregation is stronger form of association. An aggregation is a relationship between a whole and its parts.

Generalization

­A generalization is an inheritance relationship between two classes. It allows one class to inherit the public and protected attributes and operations of another class.

Realization

­Realization indicates that one class implements behavior specified by another. It is permissible for one implementation class to realize another; this means that the realizing class must conform to the interface, but need not use inheritance.

There is a sample class diagram as follows.