Problem in idoc to file mapping

Hi Experts,

I am doing a idoc to file scenario...

There is a single idoc with multiple header and line items .

I am using multi mapping for header and lineitems.

The problem i am facing is regarding the occurences in target strucure...

at which level they should be specified so all the headers come in one strucure and line items in another...or should the occurences be o to unbounded at each field level.

Kindly help me regarding the same ...