DEPARMENT is parent—EMPLOYEE is child.
There must be at least one child row for each parent at all time.
Actions on parent:
DEPARTMENT rows can only be created when a relationship is created to a child row—REQUIRES A TRIGGER.
DEPARTMENT primary keys can only be updated if at least one EMPLOYEE foreign key is also updated —REQUIRES A TRIGGER.
Can a DEPARTMENT be deleted?
YES—it is the EMPLOYEE who is required.