For relation R = (L, M, N, O, P), the following dependencies hold: { M → O, NO…
For relation R = (L, M, N, O, P), the following dependencies hold: { M → O, NO → P, P → L, L → MN }. R is decomposed into R1 = (L, M, N, P) and R2 = (M, O). The decomposition is:
Answer: B. Lossless decomposition and not dependency preserving — Conclusion: The decomposition is lossless and not dependency preserving. Lossless-join check: The intersection of the two decomposed schemas (L,M,N,P) and…
- A.
Lossless decomposition and dependency preserving
- B.
Lossless decomposition and not dependency preserving
- C.
Lossy decomposition and dependency preserving
- D.
Lossy decomposition and not dependency preserving
Attempted by 146 students.
Show answer & explanation
Correct answer: B
Conclusion: The decomposition is lossless and not dependency preserving.
Lossless-join check: The intersection of the two decomposed schemas (L,M,N,P) and (M,O) is {M}. Because the FD M → O is in the given set, M functionally determines both attributes of the second relation (M,O). Therefore the intersection functionally determines one of the relations, which satisfies the lossless-join condition. Hence the decomposition is lossless.
Dependency preservation check: The original FDs are M → O, NO → P, P → L, and L → MN. Projecting these onto the decomposed relations gives:
Onto (L, M, N, P): P → L and L → MN.
Onto (M, O): M → O.
The FD NO → P involves attributes from both relations (N and O on one side, P on the other) and is not present in either projection. It also cannot be derived from the projected FDs: using the projected FDs, the closure of {N,O} is only {N,O}, so P is not implied. Therefore NO → P is not preserved, and the decomposition is not dependency preserving.
A video solution is available for this question — log in and enroll to watch it.