Nightmare is derived from Night. Night is related to Guard. Guard is related to Occupation. 
Opening is related to Door. Door is related to Post. Post is related to Stop. one thing you do when you Shopping is Stop. 
Nightmare --DerivedFrom--> Night <--RelatedTo--> Guard <--RelatedTo--> Occupation 
Opening <--RelatedTo--> Door <--RelatedTo--> Post <--RelatedTo--> Stop <--HasSubevent-- Shopping 