The class-constraint usually2 refers to the basic-concept which is defined elsewhere. When an instance
that satisfies the class-constraint plays the role, it becomes the role-holder. For example in “a school”
context, some people play the role as a teacher (“a teacher-role”), and others play “a student-role”. People
who play “a teacher-role” and “a student-role” are called respectively “teachers” and “students” which are
role holders.