In database management systems (DBMS), redundant functional dependencies are relationships between attributes in a database that are not necessary to enforce business rules, constraints, and policies on the data in a database. They are not used to maintain the integrity, consistency, and security of the data in a database, and they can cause problems in a database, such as redundancy and anomalies.

Redundant functional dependencies occur when the value of an attribute (the determinant) is fully functionally dependent on another attribute (the dependent), and the value of the dependent attribute is fully functionally dependent on another attribute (the transitive dependent). For example, consider a database with the following attributes:

• Employee ID (determinant)
• Employee name (dependent)
• Employee salary (transitive dependent)

In this database, the employee salary attribute is redundant because it is fully functionally dependent on the employee name attribute, and the employee name attribute is fully functionally dependent on the employee ID attribute. This means that if the employee ID is known, the employee name and employee salary can be determined, and the employee salary attribute is not needed to enforce business rules, constraints, and policies on the data in the database.

Redundant functional dependencies can cause problems in a database, such as redundancy and anomalies. Redundancy is the duplication of data in a database, and it can cause problems with the integrity, consistency, and security of the data in a database. Anomalies are problems that can occur in a database when data is inserted, updated, or deleted. There are three types of anomalies: insertion anomalies, update anomalies, and deletion anomalies. Redundant functional dependencies can cause anomalies in a database because they can create conflicting data and cause problems with the integrity, consistency, and security of the data in a database.

To identify and remove redundant functional dependencies in a database, you can use the normalization process, which is the process of designing a database to reduce redundancy and eliminate anomalies. There are several normal forms that can be used to normalize a database, and redundant functional dependencies can be identified and removed in each normal form.

For example, to remove the redundant functional dependency in the above example, you can use the second normal form (2NF), which is a normal form that requires that all attributes in a database are fully functionally dependent on the primary key. To apply 2NF to the above example, you can create a separate table for the employee salary attribute and link it to the employee ID attribute using a foreign key. This will remove the redundant functional dependency and ensure that the data in the database is in 2NF.

In summary, redundant functional dependencies are relationships between attributes in a database that are not necessary to enforce business rules, constraints, and policies on the data in a database. They can cause problems in a database, such as redundancy and anomalies, and they can be identified and removed using the normalization process. To remove redundant functional dependencies in a database, you can use normal forms such as 2NF, which require that all attributes in a database are fully functionally dependent on the primary key.