An online shopping system will have objects such as shopping cart, customer, product. The shopping system will support behaviors such as place order, make payment, and offer discount. The objects are designed as class hierarchies. So for example with the shopping system there might be high level classes such as electronics product, kitchen product, and book. There may be further refinements for example under electronic products: CD Player, DVD player, etc. These classes and subclasses correspond to sets and subsets.
Sitting at her computer, a customer tries to order a book online.
Her Web browser communicates back-and-forth over the Internet with a Web server that manages the store's website.
The Web server sends her order to the order manager. This is a central computer that sees orders through every stage of processing from submission to dispatch.
The order manager queries a database to find out whether what the customer wants is actually in stock.
If the item is not in stock, the stock database system can order new supplies from the wholesalers or manufacturers. This might involve communicating with order systems at the manufacturer's HQ to find out estimated supply times while the customer is still sitting at her computer (in other words, in "real time").
The stock database confirms whether the item is in stock or suggests an estimated delivery date when supplies will be received from the manufacturer.
Assuming the item is in stock, the order manager continues to process it. Next it communicates with a merchant system (run by a credit-card processing firm or linked to a bank) to take payment using the customer's credit or debit card number.
The merchant system might make extra checks with the customer's own bank computer.
The bank computer confirms whether the customer has enough funds.
The merchant system authorizes the transaction to go ahead, though funds will not be completely transferred until several days later.
The order manager confirms that the transaction has been successfully processed and notifies the Web server.
The Web server shows the customer a Web page confirming that her order has been processed and the transaction is complete.
The order manager sends a request to the warehouse to dispatch the goods to the customer.
A truck from a dispatch firm collects the goods from the warehouse and delivers them.
Once the goods have been dispatched, the warehouse computer e-mails the customer to confirm that her goods are on their way.
The goods are delivered to the customer
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