Discussion is a type of Communication. Communication is related to Pray. Pray is related to Bless. 
Vacuum is related to Machine. Machine is related to Object. Object is related to Metal. 
Discussion --IsA--> Communication <--RelatedTo--> Pray <--RelatedTo--> Bless 
Vacuum <--RelatedTo--> Machine <--RelatedTo--> Object <--RelatedTo--> Metal 