What is the difference between Composition and Association relationship?

Question

In OOP, what is the difference between composition (denoted by filled diamond in UML) and association (denoted by empty diamond in UML) relationship between classes. I\'m a

Answer 1

Independent existence.

An Invoice is composed of line items.

What's a line item that's not on an invoice? It's -- well -- it's nothing. It can't exist independently.

On the other hand, an Invoice is associated with a Customer.

Customer has an independent existence, with or without an invoice.

If the two things have independent existence, they may be associated.

If one thing cannot exist independently, then it is part of a composition.