Division is related to Type. Type is related to Bone. Bone is related to Center. Seat is a type of Center. 
Tool is related to Level. Level is related to Difficult. Difficult is related to Challenge. 
Division <--RelatedTo--> Type <--RelatedTo--> Bone <--RelatedTo--> Center <--IsA-- Seat 
Tool <--RelatedTo--> Level <--RelatedTo--> Difficult <--RelatedTo--> Challenge 