DBMS- Generalization, Specialization and Aggregation in ER Model

Generalization:

DBMS generalization is a database modeling technique that involves creating a higher-level abstraction of similar entities in a database. It helps to simplify the database structure and improve data consistency by grouping similar entities into a single higher-level entity. The higher-level entity is referred to as a supertype, while the lower-level entities are referred to as subtypes.

For example, consider a database that contains information about employees in a company. The employees can be classified into two categories: permanent employees and temporary employees. Instead of having two separate tables for permanent and temporary employees, a generalization of the two entities into a single entity called “EMPLOYEE” can be created. The “EMPLOYEE” entity will have two subtypes: “P_EMPLOYEE” and “T_EMPLOYEE”.

DBMS generalization helps to reduce data redundancy, improve data consistency, and simplify the database structure by eliminating the need to create separate tables for similar entities. Additionally, it provides a clear and concise way to represent the relationships between entities in a database.

Specialization in a DBMS is a database modeling technique that involves creating a lower-level abstraction of a higher-level entity in a database. It is the reverse process of generalization, where a higher-level entity is divided into smaller, more specific subtypes.

For example, consider a database that contains information about employees in a company. The employees can be classified into two categories: permanent employees and temporary employees. Instead of having a single table for employees, a specialization of the “EMPLOYEE” entity into two separate entities: “P_EMPLOYEE” and “T_EMPLOYEE” can be created.

Specialization allows for the creation of more specific subtypes of entities, which can have unique attributes and relationships that are not applicable to the higher-level entity. It provides a way to represent the differences between entities in a database and can help to improve data accuracy and consistency.

In summary, specialization is a technique for creating a lower-level abstraction of a higher-level entity in a database, and it helps to improve the accuracy and consistency of data by allowing for the representation of unique attributes and relationships between entities.

Aggregation in DBMS is a relationship between two entities where one entity is a part of another entity. It is used to model a whole-part relationship between entities in a database.

For example, consider a database that contains information about a car manufacturing company. The company makes cars, and each car has multiple parts such as an engine, wheels, and a body. The “CAR” entity is the whole, and the “ENGINE,” “WHEEL,” and “BODY” entities are the parts. The relationship between the “CAR” entity and the “ENGINE,” “WHEEL,” and “BODY” entities is an aggregation relationship.

Aggregation can be represented in an E-R diagram using an oval shape with the name of the whole entity in the center and a line connecting the whole entity to the part entities.

Aggregation in DBMS helps to model complex relationships between entities in a database, and it provides a way to represent the relationship between a whole and its parts. Additionally, it helps to improve data accuracy and consistency by ensuring that the parts of an entity are properly related to the whole entity.