5. In what ways can aggregation be distinguished from composition for a whole-part relationship
Aggregation and composition are both types of whole-part relationships, but they differ in how they represent the relationship between the whole and its parts. The main ways in which aggregation can be distinguished from composition are:
1. Lifespan dependency: In composition, the parts are dependent on the existence of the whole and cannot exist independently. This means that when the whole is destroyed, the parts are also destroyed. In aggregation, the parts can exist independently of the whole and may be shared among multiple wholes.
2. Ownership: In composition, the whole owns the parts and is responsible for their creation and destruction. In aggregation, the parts are owned by external entities and can be shared among different wholes.
3. Flexibility: Aggregation offers more flexibility in terms of changing the parts or adding/removing parts, as the parts can exist independently and be shared among different wholes. Composition, on the other hand, is more rigid and changes to the parts often require changes to the whole.
4. Navigation: In aggregation, the parts can be accessed directly by external entities, whereas in composition, access to the parts is typically mediated through the whole.
5. Representation: Aggregation is often represented using a diamond-shaped line with a hollow arrowhead, while composition is represented using a filled diamond-shaped line with a solid arrowhead. This visual representation helps to distinguish between the two types of relationships in a UML diagram.