Sunday, December 9, 2018

Failure or faults?



Does software fail, or does it just have faults, or neither?
Silly questions? Not really. I've heard them for years.

Here 's the argument for "software doesn't fail":
Software always works the way it is designed to work, even if designed incorrectly. It doesn't wear out, break (unless you count corrupted files), or otherwise not perform exactly as designed. To wit: it never fails

Here's the argument for "it never fails, but has faults":
Faults refer to functionality or performance incorrectly specified such that the software is not "fit for use". Thus in the quality sense of "fit for use" it has faults.

I don't see an argument for "neither", but perhaps there is one.

However, Peter Ladkin is not buying any of this. In his blog at "the Abnormal Distribution", he has an essay, a small part of which is here:

What’s odder about the views of my correspondent is that, while believing “software cannot fail“, he claims software can have faults.

To those of us used to the standard engineering conception of a fault as the cause of a failure, this seems completely uninterpretable: if software can’t fail, then ipso facto it can’t have faults.
Furthermore, if you think software can be faulty, but that it can’t fail, then when you want to talk about software reliability, that is, the ability of software to execute conformant to its intended purpose, you somehow have to connect “fault” with that notion of reliability.

And that can’t be done.


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