Fifth Normal Form (5NF)

The 5NF (Fifth Normal Form) is also known as project-join normal form. A relation is in Fifth Normal Form (5NF), if it is in 4NF, and won’t have lossless decomposition into smaller tables.

You can also consider that a relation is in 5NF, if the candidate key implies every join dependency in it.

Example

The below relation violates the Fifth Normal Form (5NF) of Normalization −

<Employee>

The above relation can be decomposed into the following three tables; therefore, it is not in 5NF −

<EmployeeSkills>

The following is the <EmployeeJob> relation that displays the jobs assigned to each employee −

<EmployeeJob>

Here is the skills that are related to the assigned jobs −

<JobSkills>

Our Join Dependency −

The above relations have join dependency, so they are not in 5NF. That would mean that a join relation of the above three relations is equal to our original relation <Employee>.