Fifth normal form (5NF)
- A relation in the DBMS is in the Fifth Normal Form if it is in the Fourth Normal Form and does not consist of any join dependency. The joining must also be lossless for this.
- Fifth Normal Form is satisfied when all the tables present in the DBMS are broken down into as many more tables as possible to ensure that there is no redundancy.
- Fifth Normal Form is also commonly known as PJ/NF or Project Join Normal Form.
Example
|
SUBJECT |
LECTURER |
SEMESTER |
|
DBMS |
Manish |
1 |
|
DBMS |
Anil |
1 |
|
JAVA |
GP |
1 |
|
JAVA |
NK |
2 |
|
HTML |
AK |
1 |
In the table above, John takes lectures for both, math as well as computer in the first semester but does not take math in the second. In such a case, a combination of all fields in the table is needed to identify the data validity.
Now assume that we have to add another semester, where we do not know the subject or the lecturer. What do we do then? This is where Fifth Normal Form comes in. We divide the table into smaller tables.
Table1
|
Semester |
Subject |
|
1 |
DBMS |
|
1 |
JAVA |
|
1 |
HTML |
|
2 |
JAVA |
Table2
|
Subject |
Lecturer |
|
DBMS |
Manish |
|
DBMS |
Anil |
|
JAVA |
GP |
|
JAVA |
NK |
|
HTML |
AK |
Table3
|
Semester |
Lecturer |
|
1 |
Manish |
|
1 |
Anil |
|
1 |
GP |
|
2 |
NK |
|
1 |
AK |