Requirements as Goals and Commitments Too - Intentional Perspectives on Information Systems Engineering - page 146

4 Applying Goals and Commitments

We show how the conceptual model and the reasoning techniques can be used to rep-
resent and analyze a setting concerning flight tickets purchase via a travel agency.
Four main roles participate in this protocol: travel agency, customer, airline,
and shipper . Customers are interested in purchasing flight tickets for some rea-
son (e.g. holidays or business trips), travel agencies provide a tickets-selling service
to customers by booking flight tickets from airlines, shippers offer a ticket delivery
service.
Figure 4 describes the protocol in the travel agency scenario. The protocol is
defined as a set of roles (circles) connected via commitments; the commitments are
labeled ( C i ). Table 3 explains the commitments.
Figure 5 shows the situation where agent Fly has adopted the role travel agency
in the protocol of Fig. 4; the other roles are not bound to agents. Fly has one top-level
goal: selling tickets ( ticketsSold ). In order to support it, three sub-goals should be
supported: tickets should be obtained, tickets should be delivered to the customer,
and the service should be paid. Tickets can be obtained if the tickets are reserved

Fig. 4 Role model for the travel agency scenario. Commitments are rectangles that connect (via
directed arrow ) a debtor to a creditor

Ta b l e 3 Commitments in the travel agency protocol

Label Description

C 1 Shipper to travel agency : if the shipping cost have been paid,

the flight tickets will be shipped

C 2 Travel agency to customer : if the booking service has been

paid, the electronic tickets will be e-mailed

C 3 Travel agency to customer : if the booking service and the

shipping cost have been paid, flight tickets will be shipped

C 4 Airline to travel agency : if flight tickets have been paid,

tickets will be reserved

C 5 Airline to customer : if tickets have been shown, flight

boarding will be allowed