module School {

struct Address { string street;
		 string city;
		 string state;
		 short zip; };


class Person
( extent Persons
  key ssn )
{ attribute long ssn;
  attribute string name;
  attribute Address address;
};


typedef set<string> Degrees;


class Instructor extends Person
( extent Instructors )
{ attribute long salary;
  attribute string rank;
  attribute Degrees degrees;
  attribute list<Address> alternative_locations;
  attribute list< set<string> > publication_history;
  relationship Department dept
       inverse Department::instructors;
  relationship set<Course> teaches
       inverse Course::taught_by;
  long works_for ();
  short courses ( in string dept_name );
  void print ();
};


class Department
( extent Departments
  keys dno, name )
{ attribute long dno;
  attribute string name;
  attribute Instructor head;
  relationship set<Instructor> instructors
       inverse Instructor::dept;
  relationship set<Course> courses_offered
       inverse Course::offered_by;
  long avg_salary ();
  set<Course> courses ();
  void print ();
};


class Course
( extent Courses
  keys code, name )
{ attribute string code;
  attribute string name;
  relationship Department offered_by
       inverse Department::courses_offered;
  relationship Instructor taught_by
       inverse Instructor::teaches;
  relationship set<Course> is_prerequisite_for 
       inverse Course::has_prerequisites;
  relationship set<Course> has_prerequisites 
       inverse Course::is_prerequisite_for;
  set<Course> all_prereqs ();
};

};