Converting External Ship-to-party number to Internal ship-to-party number
I am working on Ale idoc scenario in which i need to create sales order from customer purchase order. for this i need to maintain ship-to-party number in advance. Customer is providing me with list of ship to party number, but i dont want to maintain external number. I wan to maintain internal ship-to-party number and assign it to external ship-to-party number coming from idoc from customer PO.
So Please suggest how can i do this. is there some standard functionality provided by sap for this, coz i think this is standard requirement.