In what situations is it appropriate to apply aggregation in object modeling?

Aggregation in object modeling is appropriate when you need to express a "part-whole" relationship, but the parts can exist independently of the whole. For example, if you have a class "Car" and a class "Wheel", then wheels can exist separately from the car (they can be replaced, used in another car). In such cases, aggregation shows that the whole object contains references to part objects but does not fully own them.

Aggregation should be used when:

• Parts can exist independently of the whole.
• To avoid strong coupling between objects.
• Flexibility in managing the lifecycle of objects is required.

Example: the "Team" class aggregates "Player" objects, but players can exist outside the team.