Index: iknow-api/Models/SemesterSubjects.cs
===================================================================
--- iknow-api/Models/SemesterSubjects.cs	(revision 70a9f6d6db7039b756db3476d3ae1155fd08d813)
+++ iknow-api/Models/SemesterSubjects.cs	(revision ea405569ef29f56fbfc4d77708b6b3faf9286097)
@@ -1,17 +1,18 @@
 namespace iknow_api.Models
 {
+    // The student is reached through EnrolledSemester.UserId; the ER model
+    // links SemestersSubjects to Users only through the professor.
     public class SemesterSubject
     {
-        public int Id { get; set; } 
-        
-        public int UserId { get; set; }                 
+        public int Id { get; set; }
+
         public int EnrolledSemesterId { get; set; }
         public int SubjectId { get; set; }
         public int ProfessorId { get; set; }
         public bool Signature { get; set; }
-        public User? User { get; set; }                 
+
         public EnrolledSemesters? EnrolledSemester { get; set; }
         public Subject? Subject { get; set; }
-        public User? Professor { get; set; }           
+        public User? Professor { get; set; }
         public PassedSubject? PassedSubject { get; set; }
     }