Aggregation […] is the typical whole/part relationship. This is exactly the same as an association with the exception that instances cannot have cyclic aggregation relationships (i.e. a part cannot contain its whole).
Composition […] is exactly like Aggregation except that the lifetime of the ‘part’ is controlled by the ‘whole’. This control may be direct or transitive. That is, the ‘whole’ may take direct responsibility for creating or destroying the ‘part’, or it may accept an already created part, and later pass it on to some other whole that assumes responsibility for it.