[SystemSafety] Modelling and coding guidelines: "Unambiguous Graphical Representation"

[paul_e.bennett at topmail.co.uk]

On 02/03/2016 at 11:22 AM, "Les Chambers" <les at chambers.com.au> wrote:
>
>Sounds interesting. The components are one thing. What about 
>emergent properties of the assembled whole. How do you review the 
>interactions. The modern zeitgeist seems to be developing systems 
>of dumb objects that interact. The problem is that the complexity 
>gets pushed into the interaction. This is an abstract thing. Very 
>hard to pick apart in a review. Have you any solutions for this?

I shall relay this in an analogy from the mechanical world.

The humble nut and bolt are a pair of components that, according to
their data-sheet will exist in a specific environment and be able to be
tightened up to a specific toque figure to serve throughout its 
designated lifetime.

We can use the nut and bolt in a more complex assembly (such as
a carburettor for a car) which will perform as indicated in the 
manufacturers data-sheet as part of the engine component.

The emergent behaviour and failure modes become known through 
the design process and with the inspection and testing that ensures
the final product is as described. Using only certified components and
frequent review stages throughout the design keeps the behaviour 
(designed or emergent) within bounds.

The entire system (the car) is designed around a multitude of 
components (probably all selected from a catalogue of components
that have proven themselves over time).

Note that this analogy is based on vehicle manufacturing before 
electronics or software became involved. The question I always pose 
is why electronics and software could not be as certain in its 
development as those early vehicle designs. 

I know it is possible as my electronics and software have survived 
with zero maintenance effort for more than 20 years (one software 
system is now operational since 1985 and has just had operational
life extension granted until 2030) within very harsh operational 
environments.

Regards

Paul E. Bennett IEng MIET
Systems Engineer

-- 
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Paul E. Bennett IEng MIET.....<email://Paul_E.Bennett@topmail.co.uk>
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