Folk is a synonym of Family. Couple is a type of Family. Couple is related to Marriage. Marriage is related to Act. 
Policeman is related to Police. Police is related to Officer. Officer is related to Agent. 
Folk <--Synonym--> Family <--IsA-- Couple <--RelatedTo--> Marriage <--RelatedTo--> Act 
Policeman <--RelatedTo--> Police <--RelatedTo--> Officer <--RelatedTo--> Agent 