Database-Management-System
August 29, 2024Database-Management-System
August 29, 2024Database-Management-System
| Question 718 |
If R(A,B,C,D) is a relation schema, which is decomposed into R1(A,B,C) and R2(C,D), which of the following ensures that the given decomposition is non additive(or lossless)?
| R1 → R2
| |
| R2 → R1
| |
| R1 ∩ R2 → R1 or R1 ∩ R2 → R2
| |
| R1 U R2 → R1 R1 U R2 → R2
|
Question 718 Explanation:
Option (C) is the correct option because a decomposition can be lossless if and only if there exists a common attribute between the decomposed relations which is either a candidate key or a key attribute in any of the decomposed tables.
For lossless decomposition:
R1 ∩ R2 → R1 (OR) R1 ∩ R2 → R1 – R2
R1 ∩ R2 → R2 (OR) R1 ∩ R2 → R2 – R1
For lossless decomposition:
R1 ∩ R2 → R1 (OR) R1 ∩ R2 → R1 – R2
R1 ∩ R2 → R2 (OR) R1 ∩ R2 → R2 – R1
Correct Answer: C
Question 718 Explanation:
Option (C) is the correct option because a decomposition can be lossless if and only if there exists a common attribute between the decomposed relations which is either a candidate key or a key attribute in any of the decomposed tables.
For lossless decomposition:
R1 ∩ R2 → R1 (OR) R1 ∩ R2 → R1 – R2
R1 ∩ R2 → R2 (OR) R1 ∩ R2 → R2 – R1
For lossless decomposition:
R1 ∩ R2 → R1 (OR) R1 ∩ R2 → R1 – R2
R1 ∩ R2 → R2 (OR) R1 ∩ R2 → R2 – R1