Relationship between classes in class diagram

What is Class Diagram?

relationship between classes in class diagram

In a class diagram, obviously you can't have classes just floating around; you need to see the relationship between them. Many have trouble. Class diagrams model the static structure of a system. They show relationships between classes, objects, attributes, and operations. Learn more. See examples. by showing the system's classes, their attributes, operations (or methods), and the relationships among objects. Class Diagram in UML Diagram Hierarchy.

Perspectives of Class Diagram The choice of perspective depends on how far along you are in the development process. During the formulation of a domain model, for example, you would seldom move past the conceptual perspective. Analysis models will typically feature a mix of conceptual and specification perspectives.

relationship between classes in class diagram

Design model development will typically start with heavy emphasis on the specification perspective, and evolve into the implementation perspective. A diagram can be interpreted from various perspectives: As we mentioned above, the class name is the only mandatory information.

Relationships in class diagrams

Relationships between classes UML is not just about pretty pictures. If used correctly, UML precisely conveys how code should be implemented from diagrams. If precisely interpreted, the implemented code will correctly reflect the intent of the designer.

Can you describe what each of the relationships mean relative to your target programming language shown in the Figure below?

relationship between classes in class diagram

If you can't yet recognize them, no problem this section is meant to help you to understand UML class relationships. A class may be involved in one or more relationships with other classes.

What is Class Diagram?

A relationship can be one of the following types: A generalization is a taxonomic relationship between a more general classifier and a more specific classifier. Each instance of the specific classifier is also an indirect instance of the general classifier.

relationship between classes in class diagram

Thus, the specific classifier inherits the features of the more general classifier. Represents an "is-a" relationship. An abstract class name is shown in italics. The figure below shows an example of inheritance hierarchy. The relationship is displayed as a solid line with a hollow arrowhead that points from the child element to the parent element. Inheritance Example - Shapes The figure below shows an inheritance example with two styles.

relationship between classes in class diagram

Although the connectors are drawn differently, they are semantically equivalent. They are represented by a solid line between classes.

UML Class Diagram Tutorial

Associations are typically named using a verb or verb phrase which reflects the real world problem domain. Simple Association A structural link between two peer classes. There is an association between Class1 and Class2 The figure below shows an example of simple association.

  • UML Class Diagram Tutorial
  • Class diagram

In the example below, the class diagram on the leftdescribes the statement of the requirement above for the static model while the object diagram on the right shows the snapshot an instance of the class diagram of the course enrollment for the courses Software Engineering and Database Management respectively Aggregation Example - Computer and parts An aggregation is a special case of association denoting a "consists-of" hierarchy The aggregate is the parent class, the components are the children classes Inheritance Example - Cell Taxonomy Inheritance is another special case of an association denoting a "kind-of" hierarchy Inheritance simplifies the analysis model by introducing a taxonomy The children classes inherit the attributes and operations of the parent class.

Class Diagram - Diagram Tool Example A class diagram may also have notes attached to classes or relationships. Notes are shown in grey.

In the example above: We can interpret the meaning of the above class diagram by reading through the points as following. Shape is an abstract class. It is shown in Italics.

relationship between classes in class diagram

Shape is a superclass. Circle, Rectangle and Polygon are derived from Shape. In other words, a Circle is-a Shape.

Relationships in UML class diagrams

There is an association between DialogBox and DataController. Shape is part-of Window. This is an aggregation relationship. Shape can exist without Window. Point is part-of Circle. This is a composition relationship.

From ERD to Class Diagram - multiple tables map to one class

Point cannot exist without a Circle. Window is dependent on Event. However, Event is not dependent on Window. The attributes of Circle are radius and center. This is an entity class.