Fire can be Useful. Fire is the opposite of Ice. Ice is related to Liquid. Acid is a type of Liquid. 
Senator is a type of Person. Person is related to Worker. Assistant is a type of Worker. 
Useful <--HasProperty-- Fire <--Antonym--> Ice <--RelatedTo--> Liquid <--IsA-- Acid 
Senator --IsA--> Person <--RelatedTo--> Worker <--IsA-- Assistant 