needed objects:

object StudentCourseRequest is 
   description: (* *)
   components: student_ID:string and title:Title and qrtr:Quarter;

end StudentCourseRequest

object Quarter is
   description: (* *)
   components: season:Season and year:integer;

end Quarter

object Season is Winter or Spring or Summer or Fall;

object StudentCourseComment is
   description: (* *)
   components: student_ID:string and title:Title and comment:string;

object StudentCourseRequestDB is StudentCourseRequest*;

object StudentCourseCommentDB is StudentCourseComment*;

operation AddStudentCourseRequest is
   inputs: rDB:StudentCourseRequestDB, r:StudentCourseRequest;
   outputs: rDB':StudentCourseRequestDB;

   pre: (* The student may not already have a course request for
           this course in the database for the selected quarter*)

        NOT ((exists rec in rDB) (rec.student_ID = r.student_ID and rec.comment = r.comment);


   post: 

        rDB' = rDB + r;
end AddStudentCourseRequest;

operation AddStudentCourseComment is
   inputs: rDB:StudentCourseCommentDB, r:StudentCourseComment;
   outputs: rDB':StudentCourseCommentDB;

   pre: (* The student may not already have a course request for
           this course in the database for the selected quarter*)

        NOT (exists r in rDB);

   post: 

        rDB' = rDB + r;
end AddStudentCourseComment;

operation ViewStudentCourseRequest is
   inputs: rDB:StudentCourseRequestDB, r:StudentCourseRequest;
   outputs: rDB':StudentCourseRequestDB;

   pre: (* The student may not already have a course request for
           this course in the database for the selected quarter*)

        NOT (exists r in rDB);

   post: 

        rDB' = rDB + r;
end ViewStudentCourseRequest;

operation ViewStudentCourseComment is
   inputs: rDB:StudentCourseCommentDB, r:StudentCourseComment;
   outputs: rDB':StudentCourseCommentDB;

   pre: (* The student may not already have a course request for
           this course in the database for the selected quarter*)

        NOT (exists r in rDB);

   post: 

        rDB' = rDB + r;
end ViewStudentCourseComment;