In my experience they're mostly expressed as states, as in "you're allowed to do this, if you're in this, this or this state" but I suppose different people model things differently.
Yes, exactly. But then you need a property or method that can return an answer to the question wich state something is in, e.g. isInThatStare() returns true or false. The point of visual modeling get a map of what your objects or classes must do. If a constraint tells you that something must be in a certain state, you must add something to be able to meet the demands of the constraint.
I didn't do a bool type because I didn't think it added enough to be worth the extra complexity.
Fair enough. That answers my original question, "Why is there no Bool Type".
As I said in the begining, this is not a 'real' problem, more of an esthetic one. I guess it's mostly a matter of how my mind works. If I add a property that I only want a true or false reply from I automaticly think "bool", and declaring it as such adds an extra confidecene that my logic is right. As mentioned above, i do not have a problem with it from a functional perspective.
I'll survive without a bool type :)