Scenario: I am being asked to create an HR training tracker for employees of a business. in this database I am using two tables: 
```
EMPLOYEE(EMPLID, LastName, FirstName, PrimaryEmail) with EMPLID as the PK, and 
```
```
SUPERVISOR(SupEMPLID) with SupEMPLID as the FK/PK.
```
[![enter image description here][1]][1]
Every instance of SUPERVISOR relates to *one and only one* instance of EMPLOYEE (because every supervisor is an employee of the company), but not every instance of EMPLOYEE exists as an instance of SUPERVISOR (because not every employee is a supervisor). 

I initially defined the relationship between EMPLOYEE and SUPERVISOR as one-to-zero-or-one [1:0,1], because again, each EMPLOYEE relates to zero or one instances of SUPERVISOR. My professor claims it is a one-to-one relationship.

Who is right here?

-------------------------------------------------[Update 1]-------------------------------------------------
1. Removed SUPERVISOR entity.
2. Created One to One-or-Many relationship between EMPLOYEE and POSITION.

[![enter image description here][2]][2]


  [1]: https://i.sstatic.net/KvWC7.png
  [2]: https://i.sstatic.net/zAkhg.png