First, we have to see the shopping cart as just another form of POS (Point of Sales system), and at the end of the business day, it needs to summarize the sales and post to the back-office.
Second, we have to assume that most of the shopping cart systems in the market are proprietary, which means we cannot hardcode the integration point into our program.
The outcome was that we developed a POS Receipts component, just another business component defined in XML files. This component allows user to enter the sales summary by any sales categories defined by user, and the transactions will just flow into the accounting normally.
This is just the starting point of POS integration. This component will be equipped with load/import function once we receive request to import some specific shopping cart data. This component will also be opened up as another web service (SOA compliant) for shopping cart software developer to consume and post the sales directly to the back-office.
These are quite easily done and thanks to the power of the DDE.