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Consider $R(I,N,W,S,Q,T,P,R)$ with $F=\{N\to W,\ IN\to S\}$.

Which of the following is the BCNF decomposition produced by successively removing these violations?

  1. $R_1(N,W)$
    $R_2(I,N,S)$
    $R_3(I,N,Q,T,P,R)$
     
  2. $R_1(N,W,S)$
    $R_2(I,N,Q,T,P,R)$
     
  3. $R_1(I,N,W,S)$
    $R_2(Q,T,P,R)$
     
  4. $R_1(N,W)$
    $R_2(I,S)$
    $R_3(I,N,Q,T,P,R)$

1 Answer

1 1 vote

Consider the first FD $:N\to W$

$N$ is not a superkey of the complete relation, so it violates BCNF.

Decompose into

$R_1(N,W)$ and $R'(I,N,S,Q,T,P,R)$.

$R_1$ is in BCNF because $N$ is its key.

Now examine $R'$.

The FD $IN\to S$ still holds.

But $IN$ does not determine $Q,T,P,R$, so $IN$ is not a superkey of $R'$.

Thus it also violates BCNF.

Decompose $R'$ into 

$R_2(I,N,S)$ and $R_3(I,N,Q,T,P,R)$.

In $R_2$, $IN\to S$, so $IN$ is a key.

$R_3$ has no non-trivial projected FD from the given set.

Therefore, the final BCNF decomposition is $\boxed{{NW,\ INS,\ INQTPR}}$

Answer : A

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