Rear is a synonym of Back. Back is related to Owe. Mortgage is a type of Owe. Mortgage is related to Agreement. 
Coal is related to Starter. Starter is part of Car. you are likely to find Computer in/at/on Car. Computer is part of Network. 
Rear <--Synonym--> Back <--RelatedTo--> Owe <--IsA-- Mortgage <--RelatedTo--> Agreement 
Coal <--RelatedTo--> Starter --PartOf--> Car <--AtLocation-- Computer --PartOf--> Network 