Next, we define predicate h(R1, R2) to indicate that the relationship between R1 and R2 is direct inheritance. Then we define r_ua(R, U) to represent that user(U) belonging to role(R) and user(U) is not inherited from other roles. Similarly, we define r_pa(R, P) to represent that role(R) has permission per(P) and per(P)is not inherited from other roles. Moreover, each role should cover the good cells as much as possible.