Hi,
I need to design a sequence diagram for the online ordering system that I will built.
This is how the system works:
-Customer displays the web page, browses the menu and adds items as she go through to the shopping basket
- once she wants to checkout, either she has to login to retrieve the contact details from the database or she has to enter it
-and if she is not already logged in she can enter a password to register while she is entering her contact details(but this is optional).
-If she wants to pay by card it forwards to paypal and gets confirmation from paypal and produces a order number to the customer or if she wants to pay by cash then it just completes the order and produces an order number to the customer.In order to pay by cash the amount should be less than £25.

You can download the png format of the diagram from here
http://www.mediafire.com/download.php?jrzmzwnmndo

thanks