Consider a schema R (A, B, C, D) and functional dependencies A → B, C → D.…
2024
Consider a schema R (A, B, C, D) and functional dependencies A → B, C → D. Then, the decomposition of R into R1 (AB) and R2 (CD), is –
- A.
Dependency preserving but not lossless join
- B.
Not dependency preserving and not lossless join
- C.
Lossless join but not dependency preserving
- D.
Dependency preserving and lossless join
- E.
Question not attempted
Attempted by 301 students.
Show answer & explanation
Correct answer: A
To determine the properties of the decomposition of R(ABCD) into R1(AB) and R2(CD), we analyze dependency preservation and lossless join. Step 1: Dependency Preservation The original functional dependencies are A → B and C → D. R1(AB) contains A → B, and R2(CD) contains C → D. Since both original FDs are preserved in the decomposed relations, the decomposition is dependency preserving. Step 2: Lossless Join For a decomposition to be lossless, the common attribute between the decomposed relations must functionally determine at least one of the relations. R1(AB) and R2(CD) have no common attributes. Therefore, there is no attribute that can ensure a lossless join. Conclusion: The decomposition is dependency preserving but not lossless join.