However, in this case there is no justification. For example, listing all the express trains is not useful. E.g., we can find out which trains are express by looking at the number component of ExpressStop . Remember that a relationship relates all the entity sets it connects. Note that the fact that employees can share phones was an intentional red herring.
Employees can share names, but no one thought to make name a class, and thank goodness for that.
Also, note that there is no purpose in making managers a subclass, since they have no special properties. No 3NF violations d. Problem 4 Each part was worth 5 points.