Aggregration - A “has a” relationship where an instance of one object/class
“has a” structural relationship with an instance of some other object type (class).
Composition - A form of “has -a” relationship where one object instance has exclusive ownership of another object instance.
= composition relationship
= aggregation relationship
Aggregation and association are recursive concepts. A composition may be
an association at one level of abstraction and an aggregation at
a higher level of abstraction.