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

[Les Chambers]

Steve

Code evaluation can sometimes be possible in unit level testing when you are
dealing with smaller code bodies, especially if you have automated tools. Of
course it should be done in the development environment. I agree with you
that it's impossible in integration and system level testing. I heard an
extreme case the other day: a Google tester related that, in his development
career, he was making a small change to some server software when he noticed
there were more than 100,000 artefacts in the build. Companies like Google
face extreme real-world conditions. The same man went to the managers of
Google server farms and laid out his machine requirements into the future
for testing. He said, "These guys were pretty blunt. They said fine, you can
have all that machine time but we'll have to shut Google down to give it to
you." So the test team came up with an innovative solution: they tested
every second mod. I hope nobody's life is on the line over a Google query.

You just can't get away from it: high-quality software is expensive.

Les

 

From: Steve Tockey [mailto:Steve.Tockey at construx.com] 
Sent: Tuesday, July 2, 2013 8:47 AM
To: Les Chambers
Cc: martyn at thomas-associates.co.uk; systemsafety at techfak.uni-bielefeld.de
Subject: Re: [SystemSafety] Qualifying SW as "proven in use" [Measuring
Software]

 

 

Les,

I think that sounds good in theory but it may not work effectively in
practice. The issue is that almost all of the test teams I know don't have
inside (aka "white box") knowledge of the software they are testing. They
are approaching it purely from an external ("black box") perspective. They
can't tell if the code has high cyclomatic complexity or not.

 

In principle, testers should be given the authority to reject a piece of
crap product. That's their job in all other industries. But in software
(non-critical, mind you), testing is usually a window dressing that's mostly
overridden if it meant threatening promised ship dates.

 

 

-- steve

发自我的 iPad

 


On Jul 1, 2013, at 2:36 PM, "Les Chambers" <les at chambers.com.au> wrote:

Steve

One way to achieve this is to empower test teams. Management issues an
encyclical that: SOFTWARE IS NOT A GIVEN. That is, "If it's too complex to
test effectively - reject it. Don't waste your time composing feckless tests
for crap software. Send it back to it heathen authors.

Kill it before it gets into production.

Les


On 02/07/2013, at 3:16 AM, Steve Tockey <Steve.Tockey at construx.com> wrote:

 

Martyn,

My preference would be that things like low cyclomatic complexity be
considered basic standards of professional practice, well before one even
started talking about a safety case. Software with ridiculous complexities
shouldn't even be allowed to start making a safety case in the first place.

 

 

-- steve

 

 

From: Martyn Thomas <martyn at thomas-associates.co.uk>
Reply-To: "martyn at thomas-associates.co.uk" <martyn at thomas-associates.co.uk>
Date: Monday, July 1, 2013 10:04 AM
Cc: "systemsafety at techfak.uni-bielefeld.de"
<systemsafety at techfak.uni-bielefeld.de>
Subject: Re: [SystemSafety] Qualifying SW as "proven in use" [Measuring
Software]

 

Steve

It would indeed be hard to make a strong safety  case for a system whose
software was "full of defects". 

High cyclomatic complexity may make this more likely and if a regulator
wanted to insist on low complexity as a certification criterion I doubt that
few would complain. Simple is good - it reduces costs, in my experience.

But if a regulator allowed low complexity as a evidence for an acceptably
low defect density, as part of a safety case, then I'd have strong
reservations.  Let me put it this way: if there's serious money to be made
by developing a tool that inputs arbitrary software and outputs software
with low cyclomatic complexity, there won't be a shortage of candidate tools
- but safety won't improve. And if you have a way to prove, reliably, that
the output from such a tool is functionally equivalent to the input, then
that's a major breakthrough and I'd like to discuss it further.

Martyn

On 01/07/2013 17:18, Steve Tockey wrote:

Martyn,
 
"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."
 
Agreed, but my fundamental issue is (ignoring the obviously contrived
cases where the defects are in non-safety related functionality) how could
software--or the larger system it's embedded in--be considered "safe" if
the software is full of defects? Surely there are many elements that go
into making safe software. But just as surely, IMHO, the quality of that
software is one of those elements. And if we can't get the software
quality right, then the others might be somewhat moot?

 

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