Help please with this problem

Draw a Business Process Diagram (BPD) to implement the following business process. The steps (textual representation) are as follows:

1. The order arrives.

2. On arrival of an order message, for every order item, check if the ordered quantity is available

in local inventory.

a. If the item is available (Yes), send item to the customer immediately.

b. If the item is not available (No), order item from the supplier. Upon arrival of the item, send it to the customer.

3. After sending an item to the customer, check if all order items have been shipped.

a. If all items have been shipped, bill the customer.

b. If all items have not been shipped, wait for items to arrive.