School
+ name+ addr- website- balance
+ staff_enrollment(staff_obj)- count_stu_num()- pay_salary()
Staff
+ name+ age- balance- salary- dept- position- school_obj
+ punch_card()
Class
+ course_obj+ semester- school_obj- stu_list=[]
Teacher
+ punch_card()+ teach_class(class_obj)
Student
+ name+ age- balance- class_obj
+ punch_card()- pay_tuition() 交学费
Course
+ name+ price- outline
BranchSchool
