Rule is a synonym of Principle. Conservation is a type of Principle. Conservation is related to Law. 
Concrete is related to Rock. Rack is etymologically related to Rock. Rack entails/necessarily involves Stretch. 
Rule <--Synonym--> Principle <--IsA-- Conservation <--RelatedTo--> Law 
Concrete <--RelatedTo--> Rock <--EtymologicallyRelatedTo-- Rack --Entails--> Stretch 