Realistic is related to Practical. Practical is the opposite of Theory. Theory is related to Fundamental. 
Guest is a type of Customer. Guest is related to Passenger. Passenger is related to Cab. 
Realistic <--RelatedTo--> Practical <--Antonym--> Theory <--RelatedTo--> Fundamental 
Customer <--IsA-- Guest <--RelatedTo--> Passenger <--RelatedTo--> Cab 