Question

Constructing Data Flow Diagrams: ATM Machine To start an ATM Withdrawal: • A card is inserted in the slot by the user, and the PIN (personal identification number) is entered. • The ATM reads information from the card, in particular, the card number and the expiry date, and accepts the PIN from the keyboard input. • The card is verified for expiry date, and then if valid, the card number and the PIN are sent to the bank for card validation by communication circuit. • The bank either sends confirmation or refusal. If confirmation is received, the user is invited to enter a transaction type. • Assuming that the transaction is a withdrawal of cash, one more validation is performed by the bank to check that the amount nominated is below or equal to the daily limit for withdrawals of 1000 AED, that the user’s weekly withdrawals do not exceed the weekly limit of 5000 AED, and that the account balance is in credit to cover the withdrawal. • If all these are OK the card is returned, the money is dispensed, and the withdrawal receipt is printed, with the date, account number, withdrawal amount and account balance. • The bank’s account records are updated to reflect the transaction. Based on the previous scenario, create the following:

a) Create a Context diagram

b) Create level zero DFD diagram

c) Select one process from level zero and develop it into level 1 diagram.

Answer 1

A level 0 data flow diagram (DFD), also known as a context diagram. So diagram for a) and b) will be same as both contains only one process node which generalizes the function of the entire system relating to external entities.

a & b

Context level dfd

c Detailed Process