Mutual exclusivity

You can define roles to be mutually exclusive either at the membership level, or at the activation level. For example:

You can define system roles, as well as user-defined roles, to be in a role hierarchy or to be mutually exclusive. For example, you might want a “super_user” role to contain the system administrator, operator, and technical support roles. Additionally, you may want to define the system administrator and system security officer roles to be mutually exclusive for membership; that is, a single user cannot be granted both roles.

See “Creating and assigning roles to users”.