To close an accounting date, all the orders must net zero. The sign on the Qty of Details is assigned with reference to this. DateTime when this order was queued for psX12 email. DateTime when this order was sent via psX12 email. For PO only, DateTime when an invoice was received via psX12 email.
Details record the 'line items' on an Order that are printed or displayed on the screen.
Reporting for Sales and Purchases also happens from the Detail lines. And, the Debits and Credits in Details are Journalized to make the vouchers posted to the General Ledger for each day's activity. In this model the Details hold all the data required for accounting. The sign on the quantity is determined by the Enterprise Engine as data input for each detail is edited. The order entry clerk should not have to be concerned with entering debits vs. credits.