Define Boyce-Codd normal form with example. How it is different that 3rd Normal form.

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BCNF (Boyce Codd Normal Form) is the advanced version of 3NF. A table is in BCNF if every functional dependency X->Y, X is the super key of the table. For BCNF, the table should be in 3NF, and for every FD. LHS is super key.


Consider a relation R with attributes (student, subject, teacher).

Student Teacher Subject
Suresh P.Naresh Java
Bipin K.Das Math
Prince P.Naresh Computer Graphics
Raju R.Prasad Computer Network

Difference between BCNF and 3NF:

The difference between BCNF and 3NF are

1. In 3NF there should be no transitive dependency that is no non-prime attribute should be transitively dependent on the candidate key. In BCNF for any relation A->B, A should be a super key of the relation.
2. It is stronger than BCNF. It is comparatively stronger than 3NF.
3. In 3NF the functional dependencies are already in 1NF and 2NF. In BCNF the functional dependencies are already in 1NF, 2NF, and 3NF.
4. The redundancy is high in 3NF. The redundancy is comparatively low in BCNF.
5. In 3NF there is the preservation of all functional dependencies. In BCNF there may or may not be the preservation of all functional dependencies.
6. It is comparatively easier to achieve. It is difficult to achieve.
7. Lossless decomposition can be achieved by 3NF. Lossless decomposition is hard to achieve in BCNF.
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