$($a$)$ The embedded software for a train ticket machine is to be developed. Use

cases have been identified for this system and the main scenario of the $$Buy

Ticket$$ use case is as follows:

$[$Precondition: the machine has tickets and a connection to the network.$]$

$1.$ The passenger requests to view available destinations.

$2.$ The system presents the available destinations for browsing.

$3.$ The passenger chooses a destination and number of tickets to buy.

$4.$ The system presents the price.

$5.$ The passenger inputs their credit card for payment

$6.$ The system contacts the card authorization service to authorize the

transaction

$7.$ The card authorization service confirms the transaction is OK

$8.$ The system dispenses tickets to the passenger.

$[$Assume that any other details of the use case are not relevant here.$]$

$($i$)$ Sketch a system sequence diagram for this scenario.

$($ii$)$ Design the realization of this scenario by assigning responsibilities to

classes and document with a communication diagram. $($Do not use a

sequence diagram.$)$

$($iii$)$ Specify how you made your responsibility assignments.