Re: Is this a simple, robust, and maintainable design?

[arkturuz]

I'd also appreciate some suggestions for improving the system.

I would suggest reversing the logic of variable names starting with 'NOT_'. It can be quite confusing to follow the logic once the whole system becomes pretty complex. So, why not name your states like 'CHECKED', 'VERIFIED', etc. and functions like 'is_checked', 'is_verified', etc. It's much easier to follow the reasoning, IMO. Notice that you don't have variables like 'NOT_BROKEN' or 'NOT_COMPLETE'.

[GrandFather]

'Negating' the NOT states actually implies the next state. The negation of NOT_CHECKED to CHECKED actually makes CHECKED semantically the equivelent of NOT_VERIFIED. I'd change the sense by changing NOT_CHECKED to NEEDS_CHECK to retain the state but to avoid the seeming double negatives scattered through the code.

[neodon]

That's pretty insightful. It would be a relatively easy change that would make everything much clearer.

[neodon]

I absolutely agree with you on this. Having negated attributes and then negating them again in conditions is pretty confusing. Thanks for pointing it out!