Enough "looking", let's do some modelling

With so much to talk about "professional communication of system's design" (such as the need for a common language, using standard and numerous viewpoints to understand the system's design model and so on), I'd almost forgotten about the stuff we're trying to communicate - the model we're making.

(And, to avoid doubt, I say "the model" in the singular, one model spanning all my eight viewpoints; although I admit now I could fall into my own trap of saying "a model", which I will mean to be the stuff needed in a model to observe it from "a" viewpoint.)

I think there are five critical ideas we need to explore if we are to feel confident in our modelling...

1. How do we manipulate the model?
2. How do we know what we're aiming at?  
3. How do we decide from which viewpoint(s) to manipulate the model, and when?
4. How formal do we really have to be?
5. What happens once we've "finished"?