Consider two entity sets A and B that both have the attribute X

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