Discover ambiguities or omissions in the following statement of requirements
for part of ticket-issuing systems:
An automated ticket-issuing system sells rail tickets. Users select their
destination and input a credit card and a personal identification
number. The rail ticket is issued and their credit card account charged.
When the user presses the start button, a menu display of potential
destinations is activated, along with a message to the user to select a
destination. Once a destination has been selected, users are requested to
input their credit card. Its validity is checked and the user is then
requested to input a personal identifier. When the credit transaction has
been validated, the ticket is issued.
Ans:
Ambiguities and omissions include:
a) Can a customer buy several tickets for the same destination together or
must they be bought one at a time?
b) Can customers cancel a request if a mistake has been made?
c) How should the system respond if an invalid card is input?
d) What happens if customers try to put their card in before selecting a
destination (as they would in ATM machines)?
e) Must the user press the start button again if they wish to buy another
ticket to a different destination?
f) Should the system only sell tickets between the station where the
machine is situated and direct connections or should it include all
possible destinations?
4.3. Rewrite the above description using the structured approach described
in chapter 4 of the textbook. Resolve the identified ambiguities in an
appropriate way.
Ans.
Function – Give customer a rail ticket, and charge credit account
accordingly
Description – Determine customer’s destination, calculate the charge for the
trip, and charge the customer the appropriate amount. If charge is
complete, print the ticket, otherwise, print no ticket, and report
error to customer.
Inputs – Destination, credit card number, personal ID number
