Fifth Normal Form (5NF)

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Fifth Normal Form (5NF) is a Project-Join Normal Form that introduced by Ronald Fagin based on Join Dependency. 5NF definition is "a table is said to be in the 5NF if and only if every join dependency in it is implied by the candidate keys. A join dependency * {A, B, ..., Z} on R is implied by the candidate key(s) of R if and only if each of A, B, ..., Z is a superkey for R."

5NF is used to decompose semantically related many non-trivial multivalued dependencies into individual non-trivial multivalued dependencies that avoid redundent data.

An instance, a Project_Employee_Task entity is maintains data through Project_Name, Employee_Name and Task_Name attributes. Project_Name, Employee_Name and Task_Name are key attributes that entity does not have any non-key attributes. The Project_Name hold Employee_Name and Task_Name, semantically the Employee_Name hold Task_Name.

Employee_Name and Task_Name are two non-trivial multivalued dependencies on the Project_Name attribute, semantically Task_Name non-trivial multivalued dependency on the Employee_Name attribute that Project_Name and Employee_Name are not a superkey of entity. These non-trivial multivalued dependencies on a non-superkey are producing redundant data.

According to the 5NF, the Project_Employee_Task entity can decompose into Project_Employee, Employee_Task and Project_Task entities to avoid redundant data. Department_Name and Task_Name are two non-trivial multivalued dependencies on the Project_Name attribute that Project_Name is not a superkey of entity.



 

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