Table: `users`; contains all similar fields as well as a `user_type_id` column (a foreign key on `id` in `user_types`
Table: `user_types`; contains an `id` and a `type` (Student, Instructor, etc.)
Table: `students`; contains fields only related to students as well as a `user_id` column (a foreign key of `id` on `users`)
Table: `instructors`; contains fields only related to instructors as well as a `user_id` column (a foreign key of `id` on `users`)
etc. for all `user_types`