Head is part of People. Head is related to Principal. Principal is a type of Educator. 
Overlook is a type of Book. Professor is a type of Book. Professor is related to Teacher. Teacher is a type of Educator. 
People <--PartOf-- Head <--RelatedTo--> Principal --IsA--> Educator 
Overlook --IsA--> Book <--IsA-- Professor <--RelatedTo--> Teacher --IsA--> Educator 