Database Normalisation Questions Long
In the context of database normalization, candidate keys refer to the attributes or combination of attributes that can uniquely identify each tuple or row in a relation or table. These candidate keys are essential in the process of normalizing a database to eliminate redundancy and ensure data integrity.
A candidate key must satisfy two properties: uniqueness and minimality. Uniqueness means that each candidate key value must be unique and cannot be duplicated within the relation. Minimality implies that no subset of the candidate key can also uniquely identify a tuple.
For example, let's consider a relation called "Employees" with attributes such as EmployeeID, Name, and Email. In this case, the EmployeeID attribute can be a candidate key as it uniquely identifies each employee. However, it is also possible that the combination of Name and Email can uniquely identify employees, making it another candidate key.
It is important to note that a relation can have multiple candidate keys, and the selection of the primary key among them is based on factors such as simplicity, stability, and performance. The primary key is chosen as the candidate key that best represents the entity and is most commonly used for referencing and joining with other tables.
During the normalization process, candidate keys are identified and used to eliminate redundancy and dependency issues. By ensuring that each attribute depends solely on the candidate key, we can achieve a higher level of data integrity and avoid anomalies like update, insertion, and deletion anomalies.
In summary, candidate keys play a crucial role in database normalization by providing unique identification for each tuple and helping in the elimination of redundancy and dependency issues. They are essential in maintaining data integrity and ensuring efficient data management within a relational database system.