Barrier is related to Wall. Wall is related to Picture. Picture is related to Background. 
Bull is a type of Policeman. Detective is a type of Policeman. Detective is a synonym of Investigator. Investigator is related to Agent. 
Barrier <--RelatedTo--> Wall <--RelatedTo--> Picture <--RelatedTo--> Background 
Bull --IsA--> Policeman <--IsA-- Detective <--Synonym--> Investigator <--RelatedTo--> Agent 