Infection is a type of Illness. Illness is related to Blind. Curtain is a type of Blind. 
Southwest is part of West. Southwest is similar to Northwest. Northwest is similar to Northeast. 
Infection --IsA--> Illness <--RelatedTo--> Blind <--IsA-- Curtain 
West <--PartOf-- Southwest <--SimilarTo--> Northwest <--SimilarTo--> Northeast 