Composition is also known as a 'is a part of' relationship because the member object is a part of the containing class and the member object cannot survive or exist outside the enclosing or containing class or doesn’t have a meaning after the lifetime of the enclosing object.
Example: If we were going to model a car, it would make sense to say that an engine is part-of a car. Within composition, the lifetime of the part (Engine) is managed by the whole (Car), in other words, when Car is destroyed, Engine is destroyed along with it.
