need to change forecast data thru planning book + doubt while creating POS

hi friends,

my application creates forecast data for following.

product , location start date , end date.

i need to put this data into APO(DP).

i know i can do it using BAPI CHANGEKEYFIGUREVALUE2 of Planning Book APs

my doubt is while create a Plng Object store, what fileds do i take as charachteristics which match these, please reply if have some clue