instance scenarios

Please see attached for more detail and correct the base use case.

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Write brief description of instance scenarios

Parent Use case name: Order book
- instance name
- Environmental conditions and assumptions
- Inputs
- Instance flow description
- output

Base use case
Use Case name: Order book
Write brief description:
- Primary actor: customer
- Brief description
- Preconditions
- Flow of events
- Post-conditons
- Alternative flows and exceptions
- Non-behavior requirements
- Assumptions
- Issue

Below is my base use case order book but I'm confusing between order book and buy book. Please help to correct it.
Use case name Order Book
Use case ID UC-200
Primary actor Customer
Secondary actor(s) Payment gateway, Shipping agent
Brief Description A customer search for books, select books, add a copy of books to the shopping cart, checks out book in the shopping cart, login account by entering email address and password, selects the shipping option, selects payment method and enters the required information.
Preconditions The customer has a valid account.
Flow of events 1. The customer enters keywords of the book. The system displays a list of books matching the keywords. 2. The customer selects a book. The system displays detailed information of the book. 3. The customer adds a copy of the book to the shopping cart. The customer can continue to search for another book. When the customer finished searching . The customer can check out the books in the shopping cart. The system asks the customer login. 4. The customers enter the email address and password. The system asks the customer to select the shipping option. 5. The customer can then select the payment method. The customer enters the required information. The system then sends the required information to the external payment gateway. The external payment gateway will send back an approval code. 6. The system confirms the transaction and sends the shipping request to the shipping agent.
Post-conditions A new order book is created and stored in the system.
Alternative flows and exceptions 1. The books asked are not in the store. 2. Fails to login 3. There is an error in the mode of payment. The balance in the customers account is not adequate to make the payment. The customer selects a new payment mode and submit the request. 4. There is an error in the shipping option selected and the customer is asked to select another option. 5. The details of the user are incorrect of information is missing, the system directs the customer to enter the missing information and resubmit the details.
Non-behaviror requirements 1. The book store responds to the request as soon as the customer login. 2. The system should not be interrupted while the transaction takes place. 3. The system cannot disable its services. 4. If there is an error in the transaction, the customer will be told. 5. The order books will be delivered. 6. The customer will always be notified if there is a problem in shipping.
Assumptions The books will be in the conditions in which they were ordered.
Issue None
Source Customer

Problem Statement of an Online Book Store:

? The Pearl River Book Company is developing an online book store system
through which its customers can buy books and sell their used books.
Public users are those who are not registered customers of the system.

? Public users or registered customers can search books by entering
keywords, which may appear in the title, author or book description.

? The system displays a list of books that matches the keywords.
? Each entry of the book list consists of the book title, author(s),
price for a new copy and price range for used copies.
? The user can select a book from the list to display more detailed
information about it (availability, price for new copy, prices for used copies,
table of contents, author, ISBN).

? The user can add a copy of the book (either new or old) to the shopping cart.
? The user can then continue to search for another book.
? When the user finishes searching, the user can checkout the books in the shopping cart.
? The system asks the user to login to his/her account by entering the
user's email address and the account password.
? If the user has not registered yet, the user can register for a new customer
account at that point.
The user enters the email address, home address and password.
The system verifies that the email address has not been used by an
existing customer before confirming the creation of the new customer
account through an email message.
The system then asks the user to select the shipping option (express, priority or ordinary). Different shipping options have different prices.
The user can then select the payment method (credit card or the user
account of the book store). If the user selects payment by credit card,
the user enters the card number, type and expiry date. The system then sends
the credit card information and the amount charged to the external payment gateway.
The amount is calculated by adding the prices of the selected books and the selected
shipping option. If the credit card transaction is approved, the external
payment gateway sends back an approval code. Otherwise, the systems
will ask the user to reselect the payment method and re-enter the
payment information. If the user selects payment by his/her account with
a sufficient balance, the system charges the amount to the customer
account. Otherwise, the system asks the user to re-reselect the payment method.
Upon completion of payment, the system arranges delivery of
the ordered books. An external shipping agent is responsible for the
delivery of the ordered books. If an order involves new books, the system
sends a shipping request to notify the shipping agent to collect the books
from the book store. New books in the same order are shipped together.
If a used book has been ordered, the system sends a delivery request to
notify the seller of the book and a shipping request to the shipping agent
of the book store. The shipping agent collects the book from the seller and
delivers the book to the buyer. Used books of the same order from the
same seller are shipped together. After the book(s) has/have been
delivered to the buyer, the shipping agent sends a shipping completion
message to the system. Upon receipt of this message, the system updates
the seller's customer account by adding the price of the used book minus
the commission charge for the service.
A public user or a registered customer wanting to sell a used book
can go through the above process by searching the book and displaying
its information. The user can then post a used copy for sale. The system
will ask the user to enter the price and the general condition of the used
book. Then the system further asks the user to enter the email address
and password of his/her customer account for login purposes. If the user
does not have a customer account, the user can create a new customer
account as described in the previous paragraph.
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