Force is a type of Act. Force is related to Electricity. Electricity is related to Rub. Rub is related to Lamp. 
Contractor is a type of Party. Party is related to Mess. 
Act <--IsA-- Force <--RelatedTo--> Electricity <--RelatedTo--> Rub <--RelatedTo--> Lamp 
Contractor --IsA--> Party <--RelatedTo--> Mess 