Service is related to Post. Post is a type of Delivery. 
Open is related to Dress. Dress is a different concept from Informal. Informal is related to Seat. Seat is related to Airline. 
Service <--RelatedTo--> Post --IsA--> Delivery 
Open <--RelatedTo--> Dress <--DistinctFrom--> Informal <--RelatedTo--> Seat <--RelatedTo--> Airline 