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Which of the following is TRUE?

  1. Every relation in 3NF is also in BCNF
  2. A relation R is in 3NF if every non-prime attribute of R is fully functionally dependent on every key of R
  3. Every relation in BCNF is also in 3NF
  4. No relation can be in both BCNF and 3NF
asked in Databases by Veteran (14.6k points)
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@ Bikram sir can you plz explain meaning of option B

 Arjun sir  Bikram  sir

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

means X->non_prime and X is key hence X is superkey also so it is in BCNF so also 3NF 

plz check 

Gate Ranker18 but here ans is c.according to u b is also correct

Gate Ranker18 in case B) non-prime-->non prime dependency is possible which is not the case in 3NF(transitive dependency)

rajoramanoj  acc to me both B and C are correct 

 reena_kandari it is X-> non_prime not  non-prime-->non prime

 every non-prime attribute of R is fully functionally dependent on every key of R

it  gurantee there should not be the case of prime--->non-prime  other than Key--->non-prime

it does not say anything about  non-prime-->non prime, so it can occure here which for sure does not gurantee 3NF.

yes correct :)

for 3nf 

LHS must be superkey OR 

RHS must be prime attribute .According to second point  key------>non prime attribute

so here second condition(non prime attribute) of 3 nf fails.lets check first condition,key must be superkey hence 3nf,but nothing about non prime which violates 3 nf 

 

 

Please explain difference between "fully functionally dependent" and "functionally dependent"

1 Answer

+21 votes
Best answer
(C) Every relation in BCNF is also in 3NF. Striaght from definition of BCNF.
answered by Veteran (332k points)
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Isn't B correct if we ignore the multivalued attributes?
Why is B incorrect , it also seems correct to me.

Nopes, that does not guarantee 3NF. For 3NF there should not be any FD X->Y such that Y-X is a non-key and X is not a super key.  

Yes, got it .  :)

It should not have transitive dependency.
can anyone explain what option b says!

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

Lets take R(ABCD)  with AB is key 

AB->C and C->D  here AB fully determine D i.e. AB-> CD

According to statement it is in 3NF but it is not. Because C->D form non prime -> non prime.

plz elaborate option B


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