Re: [SystemSafety] Qualifying SW as "proven in use" [Measuring Software]

From: Martyn Thomas < >
Date: Sat, 29 Jun 2013 16:37:21 +0100

There are, as you say, many things that have been said to aid program understanding, with some justification.

The use of strongly typed languages, for example, or avoiding the use of go-to statements, global variables, operator overloading, and inheritance.

Many programmers resist such advice and you can usually construct a situation where the deprecated language construct is the clearest and simplest way to implement a design, which makes it hard to get such advice generally adopted.

But, even if these factors and the measures that you cite could be shown to have a strong impact on defect density, they are about costs and time, not directly about safety.

The safety goal is to have sufficient evidence to justify high confidence that the software has specific properties that have been determined to be critical for the safety of a particular system in a particular operating environment. That evidence cannot depend on human inspection - it will always need automated analysis.

If the software has fewer defects introduced by the programmers and if it is easier to understand, then achieving the evidence necessary for high assurance will be more likely to succeed and require less rework and cost less. But these are quality criteria (albeit very important ones) not safety criteria.


On 28/06/2013 22:09, Steve Tockey wrote:
> That's what I've been trying to get across all along. The evidence
> that I have is that three indicators are pretty good measures [of lack
> of clarity]:
> Cyclomatic complexity
> Depth of (decision) nesting
> Fan out
> As I've said, I'm sure there are other relevant indicators as well.
> What's missing is the correlation analysis that gives us the empirical
> evidence that the indicators we look at are truly relevant. Both the
> Lorentz & Kidd and Chidamber & Kemmerer publications (cited earlier)
> proposed about 20 indicators, but I'm not aware of any serious
> correlation analysis having been done. I'm sure that most of what's in
> those publications are irrelevant, but I'm sure a couple of them are
> relevant. We just need to find a way to get the data and do the analysis.

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systemsafety_at_xxxxxx Received on Sat Jun 29 2013 - 17:37:36 CEST

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