Q7. Consider a database containing two relations: R(A,B,C) and S(D,E,F). For each of three (your choice) of the 12 rewriting rules for relational algebra expressions, give an example pair of relational

algebra expressions involving R and S such that the rewriting rule can be used to rewrite one expression to the other expression, and give another example expression pair to show the rewriting rule cannot be used since some of the conditions for the rule are not satisfied.