Hi all :I have the table Emp (EmpNum PK, EmpLastNM, EmpEducation, EmpDependent, EmpEducation,...EMpHireDate) which I want to normalize and then I want to do an ERD for it. I must break this into tables one for which , it seems, I cannot have a non-null PK: Now EmpDependent is both multi-valued and has some nulls. My question is, what can I do about setting up a PK for empdependent given the null? I have an idea of using the triple (Emp_Num, Emp_DepName, Emp_DepRelation) as the PK; an employee may have more than one dependent by the same name, but (given dependents are nuclear family) , not likely two dependents with both same name and relation. STILL, there is an employee without dependents, meaning this triple will contain some nulls. How does one usually deal with this?