Using the three class models relating to the modules discussed in Section 3.3, the system class model can be constructed. It is shown in Figure 3.5.
The compositional associations between the ViaVoice interface, GUI interface and Virtual Environment classes indicate that the system requires each of these in order to function. Removing one necessarily implies removing the others. However, the NLP modules, semantics and pragmatics, are not essential to the operation of the application. If the system were to be designed to provide only simple template pattern matching for example this could be achieved in either the ViaVoice Interface module or the Animation Interface module with almost no effort, and hence no NLP would be necessary and those module could be removed. They are therefore shown in an aggregation relationship with the ViaVoice interface and not a compositional one.
The static design of the system architecture completes the first stage of the design cycle, but in order to design a good system, the dynamic properties of the application should be understood.
