Modeling or trying to model an entire piece of software yet to be built as a bunch of UML diagrams makes little sense to me. Those diagrams are neither simulatable or nor executable, and hence aren't useful in understanding either their completeness or accuracy. The sole purpose appears to be human consumption, and if so, I prefer easy-to-produce text, which is incidentally a lot more expressive, rather than those diagrams. Or even better just go right into the programming language of your choice and code away the skeleton programs. I understand them better. My mind shuts down the moment I am required to produce a UML diagram (thankfully it happens only rarely) .
