Aggregation Vs Composition

Both aggregation and composition are words that may describe a sense of ownership. However, aggregation only implies partial ownership of something because it is composition that dictates the real type ownership of its components.

Both terms differ in the strength to which they own. This strength can be termed as bonds. In the case of aggregation, the word in itself has a weaker bond compared to composition. In composition, if all the links that binds all of its components are severed then all of the said components including the entire entity will die or collapse. In aggregation, if the links are to be destroyed then it is less likely that the entire entity will be destroyed. Its bonds may be broken but the separated aggregates can or may still exist on its own.

An example of a scenario would exist in the hospital. Each hospital has several departments like the laboratory, pharmacy, out-patient department, and emergency room amongst others. Each of these departments has its own personnel. If the hospital will be closed, all of its departments will close with it. However, this is not the case with the health personnel. They can still work at another department in a new hospital.

Hence, composition is likened to the ownership of the departments by the hospital whereas aggregation is likened to the more loose associations of the personnel to each department. It is basically a composition of hospital departments and an aggregation of department personnel. Again, as soon as the hospital closes each department dies with it because it was permanently owned by the hospital. These departments do not have the chance to transfer to another hospital nor are owned by several other hospitals.

Also, composition deals with the inside level while aggregation deals with the outer level. In this connection, it is more correct to say that a person is composed of several body organs including the heart than to claim that a person has an aggregate of organs. The heart, being one of the organs that compose a human being exists at the inner level because you cannot readily give your heart to somebody else or let your heart live by itself outside your body. Clothing can be an aggregate to the person because it is created outside and can live outside of the human body although the person and his clothing can be considered as one entire entity at some point.

Summary:
1.Composition implies real ownership of its components whereas aggregation does not necessarily own any of its aggregates.
2.Composition has a stronger bond of its components whereas aggregation has weaker or looser bonds with its aggregates.
3.Composition has components that exist at the inner level whereas aggregation has aggregates that live at the outer level.

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