Consider the following statements : I. Re-construction operation used in mixed…
2014
Consider the following statements :
I. Re-construction operation used in mixed fragmentation satisfies commutative rule.
II. Re-construction operation used in vertical fragmentation satisfies commutative rule
Which of the following is correct ?
- A.
I
- B.
II
- C.
Both are correct
- D.
None of the statements are correct.
Attempted by 201 students.
Show answer & explanation
Correct answer: B
Answer: Only the second statement is correct.
Short explanation:
Vertical fragmentation: Fragments contain different attribute subsets but share the primary key. Reconstruction is performed by joining these fragments on the key (natural or equi-join). Join is a commutative operation, so the order of joining vertical fragments does not change the result.
Mixed fragmentation: Involves both horizontal (row-based) and vertical (column-based) splits. Reconstruction may require a specific combination of union and join steps. Because the overall reconstruction uses multiple operation types and a particular sequence to restore the original relation, it is not generally safe to assume a simple commutative property for the entire mixed-fragment reconstruction.
Conclusion: The reconstruction operation for vertical fragmentation satisfies the commutative rule (so the second statement is correct). The reconstruction for mixed fragmentation is not generally commutative (so the first statement is incorrect).