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.