[SystemSafety] C for OSs

[Grazebrook, Alvery AN]

To respond to your comments:
"Back in the day, requirements elicitation was seen as a key skill of the systems analyst. Emphasis on this as a skill seems to have waned and it is, AFAI can see, often glossed over - if not entirely ignored - in much of the literature on high-integrity development."

It has definitely waned everywhere, not just in high-integrity development. The agile community seems satisfied with "user stories" that are no more and no less than WBS items. FWIW, I have almost 20 years of survey data that indicates that the biggest complaint in the development trenches is "vague, ambiguous, incomplete requirements". It is admittedly the #1 problem and yet nobody (else) seems to want to do anything about it.

I'd like to think we're doing better than this locally. One particular push is towards MBSE (Model Based Systems Engineering). We identify categories of requirements, e.g. system behaviour for a collection of functions, and create a model that expresses the intended behaviour. The tricky parts of this are:

a)     Selecting the correct level of abstraction to use for boundary (inputs, outputs, environment status). If this layer isn't managed correctly, the model of intended behaviour becomes over-constraining on the implementation.

b)    Identifying the areas of behaviour where we can't find a good way to express it in the modelling style / environment, and allowing these areas to be addressed in another way (typically through text).

Clearly, this is only an observation about one fragment of our use of MBSE.

Cheers,
            Alvery

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