[SystemSafety] Comparing reliability predictions with reality

[Robert P Schaefer]

hi,

  You have me there, I can’t speak to DAL A and would like to know more. 

  Could you reference a software engineering or computer science textbook that covers the topic?

  I assume this would be used in a grad level course.

  Do you know if there’s an equivalent for military avionics?  (doesn’t matter whose military)

bob s


> On Feb 24, 2025, at 1:38 PM, Prof. Dr. Peter Bernard Ladkin <ladkin at causalis.com> wrote:
> 
> On 2025-02-24 18:00 , Robert P Schaefer wrote:
>> My claim is, this is a very difficult business to get right safely, consistently, and in such a manner that those who come after can learn from those who came before.
> 
> I agree with that.
> 
> But some have done it.
> 
>> Not so much standing on the shoulders of giants.
> 
> Absolutely standing on the shoulders of giants.
> 
> Example. Jim Gray won the Turing Award in 1998 for his work on distributed database transactions. But he didn't solve the distributed serialisation problem under unreliable communications - 3 phase commit was still standard until Leslie Lamport solved the problem in the 1989 with the first Paxos algorithm. The entire WWW, from Amazon onwards, is now dependent on such algorithms for its functioning. Leslie won the Turing Award, amongst other things for his work on Paxos, in 2013. Leslie's Paxos algorithms have all been proved correct through use of TLA+.
> 
> You might want to say that this is not the same thing as safety software, say in civil aerospace. But it is. When DAL A software fails, the evidence is strewn over the landscape in parts (or sunk in the ocean). There is, in Derek's sense, publicly available evidence of failure. So, tell me, how many such occasions have there been in the last twenty years when DAL A software has failed?
> 
> PBL
> 
> Prof. Dr. Peter Bernard Ladkin
> Causalis Limited/Causalis IngenieurGmbH, Bielefeld, Germany
> Tel: +49 (0)521 3 29 31 00
> 
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