Consider a schema R(A,B,C,D) and functional dependencies A->B and C->D. Then…
2001
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
Answer: C. dependency preserving but not lossless join — Given: R(A, B, C, D) FDs: A → B C → D Decomposition: R1(A, B) R2(C, D) Dependency Preservation A → B is completely contained in R1. C → D is completely…
- 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
Attempted by 131 students.
Show answer & explanation
Correct answer: C
Given:
R(A, B, C, D)
FDs:
A → B
C → D
Decomposition:
R1(A, B)
R2(C, D)
Dependency Preservation
A → B is completely contained in R1.
C → D is completely contained in R2.
Therefore, all functional dependencies are preserved.
Dependency Preserving = Yes
Lossless Join Test
Common attributes:
R1 ∩ R2 = ∅
Since there is no common attribute between R1 and R2, the natural join becomes a Cartesian product, which can generate spurious tuples.
Lossless Join = No
Therefore:
Dependency Preserving = Yes
Lossless Join = No