[trustable-software] System vs component properties: Safety

Shaun Mooney shaun.mooney at codethink.co.uk
Mon Sep 10 12:16:45 BST 2018


Hi,

I totally agree. After studying the MIT work it's easy to see that it 
cuts out a lot of the main flaws with SIL based safety and making safety 
a systems design problem is clearly the way forward.

Summarising all of the STPA material and creating a re-useable, easy to 
follow tool for a safety system seems like the best thing that we can be 
doing.

Kind Regards,

Shaun


On 10/09/18 11:49, Paul Sherwood wrote:
> Hi all,
>
> I've added a small diagram to the trustable/overview [1] to highlight 
> the factors that we've so far concluded are relevant to trustability.
>
> Based on the STPA work [2], it now seems clear that safety (and 
> probably security too) have to be considered first from an overall 
> systems engineering perspective, rather than just the software 
> implementation.
>
> An OS/kernel on its own, for example, won't kill anyone. Getting a 
> 'safety certificate' for an OS therefore seems to be much more about 
> marketing than engineering.
>
> Reliability and safety are not the same, so even arguing that a given 
> piece of software is mathematically proven to meet its specification 
> doesn't guarantee safety. The specification could be wrong, the 
> hardware it runs on could misbehave, etc, and these issues outside of 
> the boundary of the software can clearly lead to actual hazards.
>
> So for the safety strand of Trustable Software, I think our most 
> useful contribution is probably to assist with spreading the word 
> about the MIT work, and helping to establish re-usable models in the 
> open for the actual hazards and safety constraints applicable to 
> example applications, e.g. Autonomous Vehicles. Do folks agree, or 
> have alternative suggestions?
>
> br
> Paul
>
> [1] https://gitlab.com/trustable/overview#readme
> [2] http://psas.scripts.mit.edu/home/get_file.php?name=STPA_handbook.pdf
>
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