How to validate safety-critical software

Question

Background: We are developing software for a small house-hold robot. Its probably not highly dangerous but it could still cause someone to fall down stairs. We are using a waterfall-like model.

Now by validation I mean answering the question: 'Did we understand correctly what our code has to do?' and not 'How to test against the requirements spec?'

In a non-safety-critical code I would build a prototype, have customer/users try it out and see if they like it. However, for safety-critical code this does not work, because it does not prove that the customer didn't forget something.

We already brainstormed possible scenarios for accidents with the customer and made sure we have requirements against what we came up with. But a more systematic approach would give us much more confidence.

Also we would like to be able to do the validation for later stages than just the requirements.

Answer 1

Another approach could be to use a Failure Modes and Effects Analysis to guide & prioritize your testing. The FMEA analysis is usually a spreadsheet, where you identify potential scenarios/flaws, then rate each on several dimensions. Usually, the probability of it happening, the consequence if it does happen, and the ability of the system to detect if its happening.

This analysis helps you prioritize testing, and maybe more importantly, potential redesign. For example, if you have a scenario that has high probably, high consequence, and no ability to detect - that is an extremely risky scenario. You should test it thoroughly, or better - redesign to reduce one or more of those dimensions (add monitoring, reduce probability, etc.)

Look up FMEA for templates. Wikipedia has a good article: https://en.wikipedia.org/wiki/Failure_mode_and_effects_analysis

Good luck!

John

Answer 2

It seems the closest government body you would want to investigate would be the FDA. They regulate medical devices as well as food & drug. If you don't have to follow this path by law, avoid it as the FDA has more power than the police to kill your business should they even suspect something is wrong. If you want to pursue this as a means of making sure you are being good corporate citizens offering a high-quality product, go ahead. You can start your investigation by searching for Medical Device Good Manufacturing Processes