Aggregation vs Composition in UML Class Diagrams

Aggregation and Composition are two important concepts in UML class diagrams that represent the relationship between classes. Understanding the difference between aggregation and composition is crucial for designing a well-structured class model.

Aggregation in UML Class Diagrams

In aggregation, one class is considered as a part of another class. It represents a "has-a" relationship where the child class can exist independently of the parent class. In UML diagrams, aggregation is represented by an empty diamond shape on the side of the parent class.

Composition in UML Class Diagrams

Composition represents a stronger form of relationship where the child class is a part of the parent class and cannot exist without it. It signifies a "contains-a" relationship. In UML diagrams, composition is represented by a filled diamond shape on the side of the parent class.

Differences between Aggregation and Composition

• Aggregation represents a weak relationship, while Composition represents a strong relationship.
• In Aggregation, the child class can exist independently of the parent class, whereas in Composition, the child class is tightly coupled with the parent class.
• Aggregation is represented by an empty diamond shape, while Composition is represented by a filled diamond shape in UML class diagrams.

It is important to carefully consider whether to use aggregation or composition in your UML class diagram based on the specific relationship between classes in your model. Using the correct relationship type will help create a more accurate representation of your software architecture.