[SystemSafety] What do we know about software reliability?

[Martyn Thomas]

Software in its operating environment does degrade over time.

  * What was fit for purpose one year no longer is the year following.
  * as vulnerabilities are discovered, shared and exploited, failure
    rates increase
  * as software is maintained to fix known errors, the fault density may
    steadily increase because the maintenance degrades the artchitecture
    and more defects are introduced. (I have seen this happen gradually
    to major software systems in my career).

The failure rates can be determined statistically within scientifically
sound confidence levels. To me, "reliability" carries the right message.
It may be an imperfect analogy but many words are.

Martyn

On 15/09/2020 14:30, Michael Holloway wrote:
> o far too many people (myself included) "reliability" necessarily
> includes notions of either randomness (for example, given an identical
> environment, history, design, and manufacturer, component A fails but
> B does not) or degradation over time.  Because neither notion applies
> to conventional software, the phrase "software reliability" is (and
> always will be) to me at best meaningless and at worst misleading.
>
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