@startuml
class Student{}
class Course{}
class Assistant{}
class TeachingAssistant{}
class CourseSubscription{}
class Appointment{}

Student "0..*" - "0..*" Course
(Student,Course) .. CourseSubscription

Course "0..*" - "0..*" Assistant
(Course,Assistant) .. TeachingAssistant

CourseSubscription "1" -- "0..*" Appointment
TeachingAssistant "1" -- "0..*" Appointment

@enduml