UGC-NET | UGC-NET CS 2017 Nov – III | Question 12

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 __________ .
(A) Dependency preserving and lossless join.
(B) Lossless join but not dependency preserving.
(C) Dependency preserving but not lossless join.
(D) Not dependency preserving and not lossless join.


Answer: (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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