Contractor is a type of Worker. Educator is a type of Worker. Educator is derived from Educate. 
Candle can be used for Burning. Burning is a different concept from Shade. 
Contractor --IsA--> Worker <--IsA-- Educator --DerivedFrom--> Educate 
Candle --UsedFor--> Burning <--DistinctFrom--> Shade 