Steel is a different concept from Iron. Iron is related to Base. Base is related to Station. 
Express is related to Super. Super is related to Market. you are likely to find Corn in/at/on Market. Corn is related to Agricultural. 
Steel <--DistinctFrom--> Iron <--RelatedTo--> Base <--RelatedTo--> Station 
Express <--RelatedTo--> Super <--RelatedTo--> Market <--AtLocation-- Corn <--RelatedTo--> Agricultural 