October 10, 2023
October 10, 2023
October 10, 2023
###### UGC NET CS 2018 DEC Paper-1
October 10, 2023
 Question 40

Consider a schema R(A,B,C,D) and functional dependencies A → B and C → D. Then the decomposition of R into R1(AB) and R2(CD) 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
Question 40 Explanation:
If the given relations are to be lossless then
R1∩R2 ≠ 0
Given R1(A,B), R2
R1∩R2 = 0

Not lossless.
The given relation decomposed into R1(A,B) and R2(C,D) and there are only two functional dependencies A→B and C→D. So the given decomposition is dependency preserving.
Question 40 Explanation:
If the given relations are to be lossless then
R1∩R2 ≠ 0
Given R1(A,B), R2
R1∩R2 = 0

Not lossless.
The given relation decomposed into R1(A,B) and R2(C,D) and there are only two functional dependencies A→B and C→D. So the given decomposition is dependency preserving.