As it is said in
ARLOW, J., AND NEUSTADT, I. UML 2 and the Unified Process, 2nd ed book, there are 7 types of relationship between different objects.
But I have read in somewhere else that if a relationship has one of the following conditions, it must be an aggregation relationship:
a) Membership b) Containment c) Assembly
The problem is I can't find out the difference between Aggregation and Containment relationship as a separate relationships!