Fifth Normal Form (5NF)

DBMSDatabaseMySQL

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>

EmpName
EmpSkills
EmpJob (Assigned Work)
David
Java
E145
John
JavaScript
E146
Jamie
jQuery
E146
Emma
Java
E147

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

<EmployeeSkills>

EmpName
EmpSkills
David
Java
John
JavaScript
Jamie
jQuery
Emma
Java

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

<EmployeeJob>

EmpName
EmpJob
David
E145
John
E146
Jamie
E146
Emma
E147

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

<JobSkills>

EmpSkills
EmpJob
Java
E145
JavaScript
E146
jQuery
E146
Java
E147

Our Join Dependency −

{(EmpName, EmpSkills ), (EmpName, EmpJob), (EmpSkills, EmpJob)}

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>.

raja
Published on 03-Jul-2018 19:34:10
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