Discover Ambiguities Or Omissions

An automatic 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 with its cost.  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.

   Ambiguities and omissions include:

Can a customer buy several tickets for the same destination together or must they be bought one at a time?

Can customers cancel a request if a mistake has been made?

How should the system respond if an invalid card is input?

What happens if customers try to put their card in before selecting a destination (as they would in ATM machines)?

Must the user press the start button again if they wish to buy another ticket to a different destination?

Should the system only sell tickets between the station where the machine is situated and direct connections or should it include all possible destinations?

What type of input device (touchscreen vs. keyboard)?

Ticket prices

Room on train (assumes tickets have times on them)

Train departure and arrival times.  Do customers buy tickets for a specific train? Or for any trip along the route?  (If the latter, then no way to tell if all the seats on a train are sold out, nor can you do seat assignments.)

Seat assignments (see above)

Print receipt?

Rewrite the above description using the structured approach described in the study text. Resolve the identified ambiguities in some appropriate way.

Function – Give customer a rail ticket, and charge credit account or take cash from customer and give the customer, a rail ticket.

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 and PIN.

Outputs – Tickets, error messages

Action – Ask the customer for their destination, when input, calculate the total, and prompt to insert a credit card, prompt customer for PIN, prompt customer that the transaction is taking place, if successful print the ticket and return to start state, if unsuccessful, ask customer to swipe their card again and re-input the PIN. If unsuccessful again, prompt that the transaction has failed, and return to start state.

Requires – Destination, credit card number and PIN

Pre-condition – None

Post-condition – None

Side effects – Charge to the customers’ credit account

Write the user requirements definitions.

The services provided for the user and the non-functional system requirements should be described. Also description may use natural language, diagrams or other nations that are understandable by customers. Product and process standards which must followed should be specified

The actors in the system are the passenger, the counter clerk and the reservation

system consisting of form processing, reservation, fare computation, ticket processing,

ticket printing, collection of fare amount and posting as sub-systems.

The passenger is a passive user-actor who initiates the process and obtains the

ticket(s), a goal of measurable value. The counter clerk is an active user-actor,

who triggers the system and has the role of issuing the tickets with the responsibility

of collecting the correct fare amount from the passenger, which is a measurable

value. Predesigned and deployed ticket reservation system at the back end is a

system actor-user to ensure that ticket processing is done correctly and different

system statuses are updated on issuing of tickets. This actor has an active role and

responsibility at the back end.

Write the system requirements specifications.

System Requirement

The passenger has a prior knowledge of the reservation and ticketing system.

The passenger arrives at the railway ticket counter and interacts with the

counter clerk first through an enquiry and then follows the process of form

filling, tendering, payment and collecting the tickets.

Passenger accepts the ticket or leaves the counter.

Passenger seeks information on fare, train timings and availability of tickets.

Passenger can have single ticket or multiple tickets.

Journey begins on a day and will be over with one break in between.

Passenger is identified by name, age, sex and address.

Trains are identified by name and number.

No receipt is issued for money transacted.

Output of the system is ticket(s) with details.

The process is triggered through a form filled by the passenger detailing the

requirements of tickets, train, date, etc.

A form is used for each train. If the journey requires use of multiple trains,

separate forms are used for each train.

Draw a sequence diagram showing the actions performed in the ticket-issuing system. You may make any reasonable assumptions about the system. Pay particular attention to specifying user errors.

Database

Ticket

System

Destination Request

Destination

Find Destination

Calculate Total

Credit Card Request

Credit Card No

Pin Request

Validate

Card

Pin

<<exception>>

Invalid Card

<<exception>>

Insufficient Credit

Charge

Card

Transacting

Print Ticket

Write a set of non-functional requirements setting out its expected reliability and its response time.

The ticket system shall respond to user inputs to provide tickets and charge accounts in a timely manner. The system shall continue to function so long as roll of ticket paper is in the machine, and a network connection is provided for the destination database and credit transactions. Upon receipt of the destination from the user, the database shall be accessed to determine the distance from the unit’s location, to the desired destination, and calculate the appropriate fee. The unit shall then prompt the user to input their card information, and the unit shall verify that the card is a credit card, is valid, and has sufficient credit to be charged. Upon successful verification, the unit shall print a ticket, and return to its ready state, for the next transaction to take place. The reliability this system relies on the durability of the physical user interface, the network connection in the area the system is placed, the size of the ticket rolls that the unit can accept, and the mechanism for dispensing the tickets. The estimated time for a complete transaction would be about thirty seconds, giving twenty for the user interactions, five for validation and verification of the users account, and five for printing and dispensing the ticket.

Develop a set of use-cases that could serve as a basis for understanding the requirements for ticket-issuing system.

Briefly describe the requirements validation process. Discuss all the checks that you have to perform to validate the above requirements in ticket-issue system

1. Customer inserts her credit card into the machine.

2. ATM checks the card number.

3. ATM asks for the pin-code.

4. User enters the pin-code.

5. ATM requests database to validate the credit card.

6. The action options are presented to the customer.

7. Customer chooses to print out account information.

8. ATM checks if enough paper is present print cartridge is not empty.

9. ATM sends request to the database.

10. ATM prints out the data and informs user of it.

11. User removes the printout from the machine.

12. Action options are presented again.

13. Customer chooses a sum from the list.

14. Customer confirms that she wants to get the selected amount of money.

15. ATM checks the physically available money.

16. ATM checks requests customer’s balance data from the database.

17. ATM requests the database to debit the customer’s account.

18. ATM returns the user’s card.

19. User picks up the card.

20. ATM provides cash.

21. User picks up the cash.

22. ATM asks the user whether she wants a receipt.

Create a semantic data model for the above scenario

Payment Processing System

Ticket Issue System

User

Interface System

What is the impact if when the customer pays cash, he is allowed not to have the exact amount?

In such case there would be a problem as to how the customer would be returned his remaining amount. Thus such cases should also be considered in designing the system.