Barrier is related to Fence. Fence requires Steal. Steal is a different concept from Buy. Buy is related to Exchange. 
Essence is related to Oil. Oil is related to Related. 
Barrier <--RelatedTo--> Fence --HasPrerequisite--> Steal <--DistinctFrom--> Buy <--RelatedTo--> Exchange 
Essence <--RelatedTo--> Oil <--RelatedTo--> Related 