UGC NET CSE | December 2014 | Part 3 | Question: 11

Question

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. 

Answer 1

Reconstruction rule of data fragmentation states that, if a relation R is decomposed into

fragments R_{1},R_{2},...R_{n}​ it must be possible to define a relational operation that will reconstruct the

relation R from fragments R1​,R2​,...Rn​. This rule ensures the constraints defined on data in the form functional

dependencies are preserved during data fragmentation.

In case of vertical fragmentation, a relation is partitioned along its attributes. In this fragmentation, the

reconstruction operation is a natural join operation, which is commutative.

In case of mixed fragmentation, a relation is partitioned along its attributes as well as along rows.

The reconstruction operation involves both union and natural join. Both operations are commutative.

In the answer keys, it is given that none of the operation is commutative.