Vehicle is related to Account. Account is related to Note. Note is related to Class. 
Trip is related to Vacation. Vacation is related to Break. Break is a type of Happen. Happen is related to Impossible. 
Vehicle <--RelatedTo--> Account <--RelatedTo--> Note <--RelatedTo--> Class 
Trip <--RelatedTo--> Vacation <--RelatedTo--> Break --IsA--> Happen <--RelatedTo--> Impossible 