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Nov2017 cs Q12

0. Consider a schema R(A, B, C, D) and following functional dependencies.
A → B
B → C
C → D
D → B
Then decomposition of R into R1 (A, B), R2(B, C) and R3(B, D) is __________ .

  • Option : A
  • Explanation :
    Schema R(A, B, C, D) is decomposed into three relation → R1 (A, B), R2(B, C) and R3(B, D) Now dependecies derived from R1 (A, B) are: A → B B → C but C is not attribute here in this relation. Dependencies derived from R1 (B, C) are: B → C C → D D is not the attribute in relation. Dependecies derived from R1 (B, D) are: D → B B → C C → D All the dependecies are preserved and it is a lossless decomposition. So, option (A) is correct.
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