Occur is a type of Appear. Pair is a type of Occur. 
Opera is related to Art. Art is related to Item. Item is related to Nose. Nose is related to Sensor. 
Appear <--IsA-- Occur <--IsA-- Pair 
Opera <--RelatedTo--> Art <--RelatedTo--> Item <--RelatedTo--> Nose <--RelatedTo--> Sensor 