Standard Use Case

1. Actors

• Customer: The individual who searches for, selects, and purchases books.

• Payment Gateway: The service that processes the payment transactions.

• Inventory System: The system that manages book stock levels.

• Shipping Service: The service responsible for delivering the book to the customer.

2. Main Success Scenario

1. Customer searches for a book:

   • The customer uses the search functionality on the website or app to find a specific book.

2. Customer selects a book and adds it to the cart:

   • The customer views the book details and adds the book to their virtual shopping cart.

3. Customer proceeds to checkout:

   • The customer initiates the checkout process by navigating to the cart and choosing to complete the purchase.

4. Customer enters shipping information:

   • The customer provides their shipping address and contact details for delivery.

5. Customer chooses a payment method and completes the payment:

   • The customer selects a preferred payment method (e.g., credit card, PayPal) and enters payment details.

6. Payment Gateway processes the transaction and confirms the payment:

   • The payment gateway verifies and processes the payment. Once successful, it confirms the transaction.

7. Inventory System updates the stock:

   • The inventory system deducts the purchased book from the available stock.

8. Shipping Service receives the order information:

   • The shipping service gets the details of the order and prepares it for delivery.

9. Customer receives an order confirmation:

   • The customer receives a confirmation message or email with the details of their purchase and estimated delivery date.

3. Extensions

Step	Branching Action	Outcome
1	Book not found: System informs customer and suggests similar or related books.	Customer is presented with alternatives or guided to refine search.
2	Selection issue: Issue with adding the book to the cart; system informs customer and prompts action.	Customer resolves issue or selects a different book.
3	Item not available: System informs customer and suggests alternatives or notifies availability status.	Customer decides to wait, choose an alternative, or cancel order.
4	Shipping information issue: System prompts customer to correct or complete shipping details.	Customer updates details and continues checkout.
5	Invalid payment details: System prompts customer to re-enter payment information.	Customer corrects payment details and retries transaction.
6	Payment fails: System informs customer of failure and allows choosing another payment method or retrying.	Customer resolves payment issue and completes transaction.
7	Inventory update issue: System informs customer of problem and attempts to rectify it.	Inventory updates once issue is resolved, or customer is informed of delay.
8	Shipping issue: System informs customer of problem with shipping and attempts to resolve it.	Customer is informed of issue and given options to resolve it.

4. Preconditions

Customer must have an active account:

• The customer needs to be logged in or have an account to complete the purchase.

Inventory System must be updated with current stock information:

• The system should reflect accurate stock levels to prevent issues with out-of-stock items.

Payment Gateway must be operational:

• The payment processing service should be functioning correctly to handle transactions.

5. Postconditions

Order is placed and payment is confirmed:

• The system registers the order and confirms that payment has been successfully processed.

Inventory is updated:

• The inventory system reflects the new stock levels after the purchase.

Shipping Service starts the delivery process:

• The shipping service initiates the process of delivering the book to the customer.

6. Special Requirements

The system must support multiple payment methods:

• The checkout process should accommodate various payment options to suit different customer preferences.

The system must comply with data protection regulations:

• Customer information, including payment details and personal data, must be handled in accordance with legal and regulatory standards.

The system must handle high volumes of traffic efficiently:

• The website or app should be able to manage large numbers of users and transactions, especially during peak times.

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