What is aggregation?
Aggregation is a collection of several things grouped together or aggregation is a special kind of association that specifies a whole or a part of relationship. For example : A \'Car\', is consisted of an engine,a steering wheel, four tires, seats, gear box, fuel tank, engine oil tank, air filters etc. So all constituents of car are parts of it. Aggregation is transitive, i.e., if A is a part of B, and B is a part of C, then A is also a part of C. Aggregation is antisymmetric, i.e., if A is a part of B, then B is not a part of A.