The Company A sells books and CDs through online shopping. The customer adds items to her shopping cart. He$/$She may cancel items or go to the check$-$out to make his $/$her purchases at any time. The customer reviews her purchases, chooses a payment method and pays. The customer may check the order status. A sales employee at company A gets the order and purchase confirmation from the system, and sends the electronic order to the warehouse. The warehouse employee updates the order status. The online shopping application will support $500$ concurrent users.