HW6: Chapter 4

4.5

• An unattended petrol (gas) pump system that includes a credit card reader. The customer swipes the card through the reader, then specifies the amount of fuel required. The fuel is delivered and the customer's account debited.

  Function:	Deliver fuel and debit customer’s account at an unattended gas pump.
  Description:	Calculate the total cost of the amount of fuel specified by the customer, then dispense the specified amount of fuel and charge the customer’s account for the calculated cost.
  Inputs:	Customer bank account information via credit card, amount of fuel required.
  Outputs:	Amount of fuel required, bill to customer’s bank account.
  Destination:	Customer’s bank account, customer’s car.
  Action:	Compute the amount to charge the customer’s bank account by multiplying the amount of fuel required by the price of fuel (ensure the units for fuel and units in price per unit are identical), send bill to customer’s bank account using calculated cost and bank account information, then dispense the amount of fuel required.
  Preconditions:	There must be room in the customer’s fuel tank for the required amount of fuel, funds for the amount of fuel required must be present in the customer’s account.
  Postconditions:	Amount of fuel delivered was subtracted from the fuel station’s reservoir, customer’s account was charged correctly, the amount of fuel required was delivered.
  Side Effects:	None.

• The cash-dispensing function in a bank ATM.

  Function:	Dispense the correct amount of cash from an ATM.
  Description:	Dispense the correct amount of cash inputted by a verified user.
  Inputs:	Amount of cash required, bank account information via debit card, PIN number.
  Outputs:	Amount of cash required
  Destination:	User
  Action:	Verify the user’s identity by matching the inputted PIN number to the bank account information from the inputted debit card. If the bank account information and PIN number combination is incorrect, stop the process and do not return any cash. If the bank account information and PIN number combination are verified, allow the user to input the amount of required cash by entering the number of each type of bank notes they want. Do not allow the user to input more cash than the ATM contains. Dispense the inputted amount of cash.
  Preconditions:	ATM contains cash, user’s bank account must contain as much or more money than cash required.
  Postconditions:	The amount of cash in the ATM decreased by the amount of required cash, the user’s bank account decreased by the amount of required cash, transaction is recorded in user’s bank account log.
  Side Effects:	None.

• In an internet banking system, a facility that allows customers to transfer funds from one account held with the bank to another account with the same bank.

  Function:	Transfers funds from one online account to another within the same bank.
  Description:	A online banking service user transfers money from their account to the account of another user who uses the same bank.
  Inputs:	Bank account information of the user who is transferring funds to another account via logging into banking service online, account number of other account to transfer funds into, amount of money to be transferred (W).
  Outputs:	Confirmation sent to both accounts.
  Destination:	Both bank accounts.
  Action:	Determine which bank account to withdraw funds from using the bank account information supplied from the logged in user’s credentials (A1), determine where to send the withdrawn funds to using the account number supplied by the logged in user (A2), debit W from A1 and credit W to A2.
  Preconditions:	The identity of A1 must be verified (must be logged in to online banking service), the inputted account number must be a valid bank account within the same bank, A1 must contain at least the amount of funds to be transferred.
  Postconditions:	A1 had W fewer funds and A2 had W more funds. The sum of both accounts remained the same.
  Side Effects:	None.

4.6

4.7