Index: iknow-api/Models/Payment.cs
===================================================================
--- iknow-api/Models/Payment.cs	(revision ea405569ef29f56fbfc4d77708b6b3faf9286097)
+++ iknow-api/Models/Payment.cs	(revision f7c8acff5e03bf7cd407218b098c5136c2ff2173)
@@ -1,16 +1,16 @@
-using System.ComponentModel.DataAnnotations.Schema;
-
 namespace iknow_api.Models
 {
+    /// <summary>
+    /// The student is reached through the enrolment: enrolled_id -> user_id.
+    /// A user_id here would be redundant and could contradict the enrolment,
+    /// which is the BCNF violation found during normalization (Phase 5).
+    /// </summary>
     public class Payment
     {
         public int Id { get; set; }
 
-        public int UserId { get; set; }
-        public User? User { get; set; }
         public int EnrollmentInfoId { get; set; }
         public int Amount { get; set; }
         public EnrolledSemesters? EnrolledSemesters { get; set; }
-
     }
 }