Partial Specialization Rule (single-line notation): specifies that an entity instance of the supertype is allowed to not belong to any subtype (ex: Faculty and staff are not the only possible types of EMPLOYEE) ??? ??? ??? Disjointness Constraint (2 rules) Disjoint Rule (letter d notation): specifies that if an entity instance is a member of one subtyp, it cannot simultaneously be a member of an