7. PGT Computer Science Question Discussion

7. PGT Computer Science Question Discussion

Which of the following is TRUE?

(A) Every relation in 3NF is also in BCNF

(B) A relation R is in 3NF if every non-prime attribute of R is fully functionally dependent on every key of R

(C) Every relation in BCNF is also in 3NF

(D) No relation can be in both BCNF and 3NF

Explanation:

Correct Answer is (C)

 

There is no confusion in option A and D that they are wrong

And there also should not any confusion in option C that is option C is correct.

In option (B) some students have confusion

So I explain that how option B is wrong

According to the definition of 2NF and 3NF

2 NF – A relation R is in second normal form (2NF) if and only if it is in 1NF and every non-key attribute is fully dependent on the primary key.

Note that it does not put any restriction on the non-prime to non-prime attribute dependency.

For Example

A--->B, B--->C , A--->C here A is key and relation is in 2NF.

Here A is Primary Key and every non key attributes i.e. B and C fully dependent on A

But here B--->C is also a functional dependency which violate 3NF

3 NF – A relation R is in third normal form (3NF) if and only if it is in 2NF and every non-key attribute is non-transitively dependent on the primary key.

In the option it is given 2NF definition not of 3NF so It is wrong