Mapping Logic

Hi all,

I have a requirement ,

my sender structure looks like

Header       1...UNBOUND

Item1          1...UNBOUND

Item2          1...UNBOUND

target structure is like

Header         1...UNBOUND

Item1            1...UNBOUND

     Field1       1...1

Item2             1...UNBOUND

here  Target 'field 1' should be mapped with 'item1' from sender .Initialy its mapped with constant 001.later it should be incremented for every occurance of Item1 in source

Thanks,

Sahana