Flat File Issue

We have flat file in the following format:
PONum    PODate       ItemID ---

PO1         05/01/2008   I1

PO1         05/01/2008   I2

PO2         05/01/2008   I1    

PO2         05/01/2008   I2

PO2         05/01/2008   I3

How to process this? I want one purchase order is one message. Also in BAM
I 
want to drill down to the item information such as quantity, upc etc. so 
Iwant to track upto item level. I will appreciate if somebody answers my 
question.