From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: *
X-Spam-Status: No, score=1.2 required=5.0 tests=BAYES_00,FROM_WORDY,
	INVALID_MSGID autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: fac41,e01bd86884246855
X-Google-Attributes: gidfac41,public
X-Google-Thread: 103376,fb1663c3ca80b502
X-Google-Attributes: gid103376,public
From: "Ken Garlington" <Ken.Garlington@computer.org>
Subject: Re: Interresting thread in comp.lang.eiffel
Date: 2000/07/14
Message-ID: <NOEb5.16337$7%3.1009209@news.flash.net>#1/1
X-Deja-AN: 646318593
References: <8ipvnj$inc$1@wanadoo.fr> <8j67p8$afd$1@nnrp1.deja.com>
 <slrn8leffq.ebq.gisle@spurv.ii.uib.no>
  <395886DA.CCE008D2@deepthought.com.au> <3958B07B.18A5BB8C@acm.com>
  <y1d65.620$7%3.33446@news.flash.net> <395A0ECA.940560D1@acm.com>
  <8jd4bb$na7$1@toralf.uib.no> <8jfabb$1d8$1@nnrp1.deja.com>
 <8jhq0m$30u5$1@toralf.uib.no> <8jt4j7$19hpk$1@ID-9852.news.cis.dfn.de>
 <3963CDDE.3E8FB644@earthlink.net> <8k5alv$1oogm$1@ID-9852.news.cis.dfn.de>
 <Rmt95.7825$7%3.595826@news.flash.net>
 <8kl25k$2q7k0$1@ID-9852.news.cis.dfn.de>
X-Priority: 3
X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2919.6600
X-Complaints-To: abuse@flash.net
X-Trace: news.flash.net 963582253 216.215.75.113 (Fri,
 14 Jul 2000 08:44:13 CDT)
Organization: FlashNet Communications, http://www.flash.net
X-MSMail-Priority: Normal
NNTP-Posting-Date: Fri, 14 Jul 2000 08:44:13 CDT
Newsgroups: comp.lang.ada,comp.lang.eiffel
Date: 2000-07-14T00:00:00+00:00
List-Id: <comp.lang.ada>

"Joachim Durchholz" <joachim dot durchholz@halstenbach.com> wrote in message
news:8kl25k$2q7k0$1@ID-9852.news.cis.dfn.de...
> Ken Garlington <Ken.Garlington@computer.org> wrote:
> > "Joachim Durchholz" <joachim dot durchholz@halstenbach.com> wrote:
> > > In other words: had DbC been applied not only to the software but
> also
> > > the the software-IRS interface,
> >
> > What do you mean by a software-IRS interface?
>
> The IRS is a piece of hardware from the point of view of the main
> controlling software of the Ariane, right?
>
> > And why is this interface relevant to the Ariane 5 disaster?
>
> The system crashed because the IRS flooded that interface with
> meaningless data, right?

Going back to your original statement, which was:

> In other words: had DbC been applied not only to the software but also
> the the software-IRS interface, then the programmer doing the
> integration would have seen the contract and would have had a chance to
> see the inconsistency between IRS specification and flight trajectory
> data.

Assuming that the IRS-side contract would have been with respect to range,
as in:

-- the contract from the IRS side
IRS_write_value (horizontal_bias: INTEGER) is
      require
         horizontal_bias <= 32767
      do
         ...

      ensure
         written_value <= 32767

      end

and given what the OBC would expect, as in:

OBC_read_value (void) return INTEGER is
  require
  do
     ...
  ensure
       read_value <= 32767
  end

This certainly wouldn't denote any inconsistency as far as I can tell,
particularly since on a MIL-STD-1553 bus it's physically impossible to
violate this contract!

So, once again, you can't simply assert the magic of DbC in the context of
Ariane 5. You have to (for a start) give a specific contract that would have
made it clear that there was a problem. After all: "the official report is
clear and detailed enough to enable software professionals, aerospace
experts or not, to form their own judgment."