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DBMS 5NF

DBMS 5NF with DBMS Overview, DBMS vs Files System, DBMS Architecture, Three schema Architecture, DBMS Language, DBMS Keys, DBMS Generalization, DBMS Specialization, Relational Model concept, SQL Introduction, Advantage of SQL, DBMS Normalization, Functional Dependency, DBMS Schedule, Concurrency Control etc.

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Fifth normal form (5NF)

  • A relation is in 5NF if it is in 4NF and not contains any join dependency and joining should be lossless.
  • 5NF is satisfied when all the tables are broken into as many tables as possible in order to avoid redundancy.
  • 5NF is also known as Project-join normal form (PJ/NF).

Example

SUBJECT LECTURER SEMESTER
Computer Anshika Semester 1
Computer John Semester 1
Math John Semester 1
Math Akash Semester 2
Chemistry Praveen Semester 1

In the above table, John takes both Computer and Math class for Semester 1 but he doesn't take Math class for Semester 2. In this case, combination of all these fields required to identify a valid data.

Suppose we add a new Semester as Semester 3 but do not know about the subject and who will be taking that subject so we leave Lecturer and Subject as NULL. But all three columns together acts as a primary key, so we can't leave other two columns blank.

So to make the above table into 5NF, we can decompose it into three relations P1, P2 & P3:

P1

SEMESTER SUBJECT
Semester 1 Computer
Semester 1 Math
Semester 1 Chemistry
Semester 2 Math

P2

SUBJECT LECTURER
Computer Anshika
Computer John
Math John
Math Akash
Chemistry Praveen

P3

SEMSTER LECTURER
Semester 1 Anshika
Semester 1 John
Semester 1 John
Semester 2 Akash
Semester 1 Praveen

Next TopicDBMS Relational Decomposition




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