What is aggregation? (C++)

Aggregation is a strong form of association in

Which an aggregate object is made component.

Components are part of the aggregate. The aggregate is   an extended object that is treated as a unit in many operations, although physically it is made of several lesser objects.

A single aggregate object may have several parts. Each part-whole relationship is treated separate aggregation in order to emphasize the simplicity to association. Aggregation is inherently transitive; an aggregate has parts, which may in turn   have parts.

Aggregation Versus Association

Aggregation is a special form of association, not an independent concept. Aggregation adds semantic can notation in certain cases. If two objects are tightly bound by apart-whole relationship, it is an aggregation.

If the two objects are usually considered as independent, even though they may often be linked. It is an association some tests include:

(i)Would you use the phrase part of?                    

(ii) Are some operations on the whole automatically applied to its parts?

(iii) Are some attribute value propagated from the whole to all or some parts?

(iv)Is there an intrinsic asymmetry to the association, where one object is subordinate to the other ?