BDC for ME21

Hi All,

I need to create a BDC for the creation of Purchase orders using t-code ME21. but each PO may have different items i.e if one Po have 2 items other PO may have 5 items. so how to do this.

How can i upload the data of the different PO's in BDC. How should the flatfile should be designed??

Regards

Sudhir