Grave is related to Dark. Dark is related to Hide. Cave can be used for Hide. Cave is related to Hole. 
Bar is related to Joint. Joint is related to Elbow. Elbow is related to Bend. 
Grave <--RelatedTo--> Dark <--RelatedTo--> Hide <--UsedFor-- Cave <--RelatedTo--> Hole 
Bar <--RelatedTo--> Joint <--RelatedTo--> Elbow <--RelatedTo--> Bend 