RDBMS Interview Question:

What do you understand by dependency preservation?

Submitted by: Administrator

Given a relation R and a set of FDs F, dependency preservation states that the closure of the union of the projection of F on each decomposed relation Ri is equal to the closure of F. i.e.,
((?R1(F)) U … U (?Rn(F)))+ = F+
if decomposition is not dependency preserving, then some dependency is lost in the decomposition.
Submitted by: Administrator