Q1. Aggregation and Composition

A1. Aggregation means a container for a collection of objects. A metaphor here is a Java Hashtable. It contains the references to one or many objects.

      Composition means an element or ingredient of an object. For example, an object A could have an object B as its member data in the form of value (Not a reference)

The value object is a composition, the reference object is a aggregation.