Person HAS A IEmploymentRelationship
ContractEmployment IMPLEMENTS IEmploymentRelationship
FullTimeEmployment IMPLEMENTS IEmploymentRelationship
FullTimeEmployment HAS A IDirectReport
Manager HAS A Person
Manager IMPLEMENTS IDirectReport
And then salary() is a polymorphic function declared by the IEmploymentRelationship interface, where FullTimeEmployment instances use the manager somehow, and ContractEmployment doesn't.
You can even put some sugar on that by having a salary() function on Person that calls the salary() function on its IEmploymentRelationship—but I wouldn't, for the same reason I wouldn't denormalize a relational database.
You can even put some sugar on that by having a salary() function on Person that calls the salary() function on its IEmploymentRelationship—but I wouldn't, for the same reason I wouldn't denormalize a relational database.