[SystemSafety] Does "reliable" mean "safe" and or "secure" or neither?

[Roberto Bagnara]

On 24/04/2016 11:13, Michael J. Pont wrote:
> Overall, I think this is a great list (and I think that PBL deserves a medal
> for the work he does on it).

I think the same.

> In terms of the most recent discussion (that gave rise to your comment),
> "software reliability" doesn't make sense to me as a label (because the
> software does not change / wear out).

Please help me understand.  Suppose we have a system that is composed
by a number of interacting components.  Suppose also that such components
are black boxes: we cannot look inside them.  However, we know
everything about the interactions between the components because we can
monitor them with precision.  Suppose we also have specifications
of each component that are detailed enough so that, in case of system
failure/misbehavior, we are able to point the finger at small sets
of components and tell which component(s) originated the first out-of-spec
behavior, which component(s) that were meant to mitigate this misbehavior
failed to do so, and so on.

My question is:

  Can we talk about the reliability of the components in the context
  of the overall system, without any knowledge about how they implement
  their functionality (e.g., hardware only, hardware + little bit of
  software, hardware + lots of software, hardware + software + humans)?

Kind regards,

    Roberto

-- 
     Prof. Roberto Bagnara

Applied Formal Methods Laboratory - University of Parma, Italy
mailto:bagnara at cs.unipr.it
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