Soap is related to Sink. Sink is a type of Clean. Clean is related to Wipe. 
Merchant is related to Seller. Seller is related to Buyer. Buyer is a type of Customer. 
Soap <--RelatedTo--> Sink --IsA--> Clean <--RelatedTo--> Wipe 
Merchant <--RelatedTo--> Seller <--RelatedTo--> Buyer --IsA--> Customer 