Subtyping separates shared person data from role-specific data. A People entity can hold First Name, Last Name, and Email for salespeople, customer contacts, supplier contacts, and sales area managers. A specialized entity then stores attributes that apply only to one role. section 4.1.3
A practical rule is to move common attributes into the supertype and keep unique attributes in the subtype. For example, Sales Persons can join back to People while retaining Sales Target and Employee Number. This avoids repeating the same person details across several role entities. section 4.1.3
Person and employee roles
People is the supertype; Sales Persons is a subtype with sales-only fields. The AdventureWorks sample database uses the same pattern: Employees is a subtype of Person. section 4.1.3
