For the two use-cases provided below for a Web Banking System: use case PayBills and AccountOverdraft :

a) Draw a sequence diagram showing the successful payment of a bill. You may assume that the Web Customer is already logged in.

b) Select an operation of your choice used in the sequence diagram from and express its contract in English. Do you need to make any changes to the sequence diagram in order to ensure that the contract is met?

Use case PayBills of the system, Brief Description: Precondition Primary Actor Secondary Actors Bank Dependency Generalization Web Customer pays bills through the Bill Payment Web Customer is Web Customer in. Web Customer selects the EXTENDED BY USE CASE AccountOverdraft None Basic Flow Step # The system displays the Bill Payment page containing the list of registered bills and bank accounts of Web Customer Web Customer selects bills to be paid through the system. Web Customer enters the amount to be paid through the system. IF Web Customer does not want to pay the bills on the current date THEN Web Customer enters the dates to pay the bills through the system ENDIF The system VALIDATES THAT the dates of the entered bill payments are correct. The system requests confirmation of the amounts and dates of the entered bill payments. IF there are errors in the amounts and dates of the entered bill payments THEN Web Customer corrects the amounts and dates of the entered bill payments ENDIF Web Customer confirms the amounts and dates of the entered bill payments through the system DO Step # IF the payment date is immediate, THEN the system communicates with Bank to transfer the bill amount from the bank account of Web Customer to the utility's bank account ELSE the system asks Bank to add the bill payment to the list of in of Web Customer ENDIIF UNTIL all bill The system receives a transaction record including a confirmation number to track the bill ents are s to from Bank. The system displays the notification of successful bill payments showing the confirmation number of the transaction record for each payment. Web Customer terminates the Bill payments page through the system. Postcondition:The system displays the Account Summary Pa Specific Alternative Flows: RFS RFS Basic Flow Step 2) 3) The system rejects the entry The system prompts Web Customer to re-enter a valid date RESUME BACK TO 4 Postcondition: None