ME test

Question

Which of the following statement false of relation R is in 3NF but not BCNF?

 

A.Relation R must consist atleast two over-lapped candidate keys.

B.Relation R must consist proper subset of candidate key determines proper subset of some other candidate key.

C.Relation R must consist atmost one compound candidate key and other candidate keys simple candidate key.

D.Relation R must consist atleast two compound candidate keys.

Comments

a relation R in 3NF but not in BCNF iff proper subset of some candidate key determines proper subset of some other candidate key. comparing this statement with the given statements, we got that C is incorrect.

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suppose we have R(ABCD).  given AB,CD as 2 candidate keys.

there is one extra functional dependency

D->B(here r.h.s. is prime attribute) so it is in 3NF but not in BCNF .so how option A evaluates to true.as we have 2 non overlapped candidate keys here.

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what are the other FDs in your example?

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AB->C

AB->D

CD->A

CD->B

D->B

where am i going wrong?