Draw a use case diagram for a ticket distributor for a train system. The system includes two actors: a traveler, who purchases different types of tickets, and a central computer system, which maintains a reference database for the tariff. Use cases should include: BuyOneWayTicket, BuyWeeklyCard, BuyMonthlyCard, UpdateTariff. Also include the following exceptional cases: Time-Out (i.e., traveler took too long to insert the right amount), TransactionAborted (i.e., traveler selected the cancel button without completing the transaction), DistributorOutOfChange, and DistributorOutOfPaper.

This questions can have several correct answers, Figure 2-1 being a possible answer. The following elements should
be present:
• The relationship between an actor and a use case is a communication relationship (undirected solid line).
• The relationship between exceptional use cases and common use cases is an <> relationship.
• The exceptional use cases described in the exercise only apply to the use cases invoked by the traveler.
The following elements should be present in a “good” answer:
• All exceptions apply to all traveler use cases. Instead of drawing 3x4 relationships between these use cases, an
abstract use case from which the exceptional use case inherit can be used, thus reducing the number of
<> relationships to 3 at the cost of introducing 4 generalization relationships.
• The student can introduce exceptional use cases not specified in the exercise that apply to the
CentralComputerSystem use cases.