What is the difference between aggregation and association in DBMS?

Answer 1

In the realm of Database Management Systems (DBMS) and Object-Oriented Design, understanding relationships between entities or classes is paramount. Two of the fundamental relationships discussed are Association and Aggregation in DBMS.

Association: At its core, association is a simple bi-directional relationship between two classes or entities. It signifies that they are related in some way, but without any ownership implication. For instance, consider a 'Teacher' and 'Student' relationship. A teacher teaches students, and students learn from a teacher. This mutual relationship is an association, where neither entity owns the other.

Aggregation: This relationship takes association a step further by introducing the concept of ownership or a "whole-part" relationship. In aggregation, one class (the whole) contains or is composed of other classes (the parts). However, the lifecycles of the contained classes are independent of the container. Imagine a 'Library' and 'Book' relationship. A library contains books, but if the library ceases to exist, the books don't necessarily get destroyed.

A critical distinction is the lifecycle implication. In pure association, there's no ownership, and thus, the lifecycle of one entity doesn't impact the other. In aggregation, while there's a clear ownership, the contained entity's lifecycle remains independent.

In practical applications, understanding these relationships helps in crafting efficient database schemas and object-oriented designs. It aids developers in visualizing data interactions, ensuring that systems are both robust and scalable.

Answer 2

In DBMS, aggregation is a relationship where one object contains another object, indicating a whole-part relationship. Association is a relationship between two separate entities, showing how they are connected. Aggregation implies that the contained object can exist independently, while association does not imply any part-whole relationship.

Answer 3

Association

Association is a relationship between two objects. In other words, association defines the multiplicity between objects. You may be aware of one-to-one, one-to-many, many-to-one, many-to-many all these words define an association between objects. Aggregation is a special form of association. Composition is a special form of aggregation.

Example: A Student and a Faculty are having an association.

Aggregation

Aggregation is a special case of association. A directional association between objects. When an object 'has-a' another object, then you have got an aggregation between them. Direction between them specified which object contains the other object. Aggregation is also called a "Has-a" relationship.