 A model of a distributed system in this framework will actually be a model of a kind of distributed system, hence the model of the radar-airplane system that we will use as a running example here will actually be a model of radar-airplane systems (in plural). Setting such a model requires describing the architecture of the system in terms of its parts and the way they are put together into a whole. Once that is done, one can proceed to see how that architecture enables the flow of information among its parts. 