The method by which the three application modules in Figure 3.1 shall interact, will follow the asynchronous model of communication.
The signal/slot method of asynchronous communication shall be implemented, whereby signals are connected to handlers in a many to many relationship, with only the signal marshaler knowing which handlers are connected to each signal.
The major advantages of this approach are that each module can run in effective isolation, only asking for the information it needs and only giving out the data it is asked for. No prior knowledge about the source of the requested information is needed and, similarly, neither is information about how it shall be derived, required. What's more, each module is free to provide requesters of its information in anyway it sees fit.
This asynchronous signal/slot method also allows great flexibility during development due to the level of code separability that is possible. Namely, each module can be developed in isolation since it has freedom over the methods it employs, as long as the interface slots and signals remain constant.