Discover ambiguities or omissions in the following statement of requirements for
part of a ticket-issuing system:
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
Ambiguities and omissions include:
1. How should the system respond when a user presses the start button?
2. What happens if a user tries to buy several tickets for the same destination
3. At what step are users requested to input a personal identifier?
4. Can users cancel a request if a mistake has been made?
5. How should the system respond if an invalid card is input?