readers are referred to Rumbaugh's book on object modelling. Briefly,operations are identified by modelling event scenarios for the different functions provided by the systems.The events are then traced to object that react to them. Typical scenarios model the interactions between the users and the system. Events representing the user interactions are shown arriving at the system interface, and the system responses leaving it.Figure 6.17 show a typical event continuous arrows and exceptions as broken arrows.Events are also number to show their sequence.
The library loan functions is initiated by the user requesting a library item. The library assistant scans the user registrations into the system for verification.The system responds by accepting the user registration or rejecting it(see event 3).If the system accepts the registration,the library assistant verifies that the item can be loaned to the particular user. If the system accepts the request,the item is loaned.
In the next section we will briefly describe four object-oriented methods;namely the Shaler-Mellor method, the object-oriented analysis(OOA),the objec modeling technique(OMT) and the Jacobson method. We will high-light the similarities and the differences between the methods.Other methods