Model the following business process at a supplier.
After a supplier notifies a retailer of the approval of a purchase order, the supplier can either receive an order confirmation, an order change or an order cancellation from the retailer. It may happen that no response is received at all. If no response is received after 48 hours, or if an order cancellation is received, the supplier will cancel the order. If an order confirmation is received within 48 hours, the supplier will process the order normally. If an order change is received within 48 hours, the supplier will update the order and ask again the retailer for confirmation. The retailer is allowed to change an order at most three times. Afterwards, the supplier will automatically cancel the order.