#test_ace

Question

Find the FD for relation schema R(A,B,C,D) with pimary key AB under which R is in 2nf but not in 3nf

A)  AB->CD, A->C, C->D

B) AB->CD, B->C, C->B, A->D

C) AB->CD, C->D, DB->AC

D) AB->CD, BC->D

Comments

It should be option D.

Where no partial dependency

but in BC->D

LHS is not Key or RHS is not any PA.

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Any explanation for C

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In option C,

Keys are AB, DB, CB

Hence AB->CD (LHS is key)

DB->AC (LHS is Key)

C->D (RHS is PA)

Hence it is in 3NF

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@  Ashwin Kulkarni 

In option C

Keys are: AB, DB, CB