Type the EMPLOYEE supertype with its three subtypes (attribute placement).

Answer

EMPLOYEE(Employee_Number, Name, Address, Date_Hired) HOURLY_EMPLOYEE(Hourly_Rate) SALARIED_EMPLOYEE(Annual_Salary, Stock_Option) CONSULTANT(Billing_Rate, Contract_Number)

Shared attributes (incl. the identifier Employee_Number) sit on the supertype; each subtype lists only what is unique to it. A CONSULTANT instance inherits the four EMPLOYEE attributes and adds two of its own — zero nulls, zero repetition.