Embedded software DbC

[bearophile]

Kagamin:

> > In the situation like the one of the Ariane I think the good solution is the introduce a fuzzy control system that has a degradation of its effectiveness as conditions come out of its specs, but avoids a total failure. This is what biological designs too do. It's a kind of 'defensive programming'.
> > 
> From what I heard, the software for Ariane was physically unable to handle Ariane, so no matter what assertions you put into it, it would crash.

In that last paragraph I was talking about something that doesn't use assertions, something like:
http://en.wikipedia.org/wiki/Fuzzy_Control_System

If well designed such systems have a graceful degradation of functionality even when you step out of their specs. Systems like this are used today in critical systems like breakers control systems of subway trains where a sharp shutdown like the one on the Ariane can cause hundred of deaths. When well designed such fuzzy systems do work very well. All this is kind of the opposite of the design strategy behind DbC :-)

My theory is that DbC is good to design and test critical systems because it allows you to spot and fix design bugs efficiently. But when the critical system is working, it's better to put beside it another system that shows graceful degradation and doesn't just stop working abruptly when some parameter is outside its designed specs. This is how most control systems in vertebrate brains are designed, they generally never just shut down.

Bye,
bearophile