title: How to resolve this normalization issue in ER diagram
body: <p>This is academic so please, no comments that in real world it is not done like that :)</p>
  
  <p>The point of this exercise was to normalize as much as possible.</p>
  
  <p>The point is: An Employee can have 1 role (but 1 role can be assigned to more employees). A role can be either Reg.Employee or Lead, again these can be assigned to more roles (not repeating values) That is the problem as the Role would hold two FKs (one to Reg.Employee and the other one to Lead) but both would need to be nullable, righ? If I make one nullable, when creating a record for the other one, I would need to assign this role as well. So I assume in the ERD abstraction, the only way would be to make both FKs nullable.
  <img src="https://i.stack.imgur.com/Am1M6.png" alt="enter image description here"></p>