Consider two entity sets A and B that both have the attribute X (among others whose names are not relevant to this question). a. If the two Xs are completely unrelated, how should the design be improved? b. If the two Xs represent the same property and it is one that applies both to A and to B, how should the design be improved? Consider three subcases: X is the primary key for A but not B X is the primary key for both A and B X is not the primary key for A nor for B