I decided to make (generally) Sundays holidays for this blog. It's good to have holidays.
One short note however: in my posts so far and from now on, I am using the terms "models" and "specifications" internchangeably --- both are used informally to denote descriptions of behaviour which pick up some specific interesting aspects of software which you are making (interesting for you!).
So models do not have to be formal, they can even be a rough pictorial sketch of structures of systems you are going to make, even just a stroke of a red line which is something meaningful for you. Of course one problem of such an informal sketch is when you look it again later you may have forgotten what it meant.
So if such description --- may it be called a specification or a model --- is written in a clearly understandable way, and even in an unambiguous way, then it is useful, you can read it again to remember what you were thinking, other designers can read it and understand your intention, get hints how it can get updated and evolve.
That's why it is good to have a language, graphical or textual or otherwise, for neatly and clearly describe your non-executable ideas.
(The term "specification" has a connotation of formalism, verification, etc. .. which are surely some of the possible things we can do for non-executable descriptions: but they are far from all we wish to do with models and specifications, for example clarity is a virtue in both formal and informal descriptions.)
