The Path Column

        "|manufacturer|brand|model"
                     |
          |<----------
        path,audience_size,cpm,buyable
        "|General Motors","","",0
        "|General Motors|Chevrolet",1000000,0.80,1
        "|General Motors|Chevrolet|Spark",100000,0.15,1
        "|General Motors|Chevrolet|Sonic",150000,0.20,1
        ...
        "|General Motors|Cadillac",150000,1.00,1
        "|General Motors|Cadillac|Coupe",150000,0.30,1
        "|General Motors|Cadillac|Sedan",150000,0.35,1
        ...