Letter is a type of Owner. Letter is related to Object. Object is related to Plate. you are likely to find Sandwich in/at/on Plate. 
Variety is related to Vary. Vary is related to Change. Tighten is a type of Change. 
Owner <--IsA-- Letter <--RelatedTo--> Object <--RelatedTo--> Plate <--AtLocation-- Sandwich 
Variety <--RelatedTo--> Vary <--RelatedTo--> Change <--IsA-- Tighten 