RE: [sc] sc: languages



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From: Simon Hughes (Simon.Hughes(at)era.co.uk)
Date: Fri 14 Jun 2002 - 12:14:26 BST


Martyn Thomas asked:

> 1)	Why do people program in C when SPARK is demonstrably 
> so much safer?

I don't know why people choose C over SPARK (I've never had to make that
decision myself) and I'm not familiar with literature comparing the two
languages but I can't help wondering if a few questions might lead to one or
two possible answers ...

What does it mean to claim that SPARK is "demonstrably so much safer" than
C?  Does it mean that identical systems, apart from choice of programming
language have been developed and operated, and one has led to fewer
fatalities/injuries?

The rest of this email assumes not.

Does it mean that functionally identical softwares have been developed and
one is "better" than the other, e.g. has been shown to contain less faults?

If so, how often has this been done?  Can it reasonably be claimed that all
possible kinds of safety-related softwares one might want to develop have
been covered?  If not, isn't it possible that there are certain
safety-related softwares for which SPARK is either not appropriate or
possibly "worse" than C?

Has it been shown that whatever makes SPARK "better" than C has a
significant effect on safety ("so much safer")?  I'm no expert on languages
or language selection, but it seems plausible to me that choice of language
need not have that much effect on safety, even though it may have a big
effect on other attributes, e.g. no. of faults?  Hasn't this been claimed by
others, backed up by studies, etc?

Simon

---------------------------------------------------------------------
Dr Simon Hughes, Senior Consultant Engineer
Safety and Reliability Group, ERA Technology Ltd,
Cleeve Road, Leatherhead, Surrey, KT22 7SA, UK
Phone: +44 (0)1372 367448    Fax: +44 (0)1372 367072
Email: simon.hughes(at)era.co.uk   WWW: http://www.era.co.uk/


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