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=0.2 required=5.0 tests=BAYES_00,INVALID_MSGID, REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: fac41,2c6139ce13be9980 X-Google-Attributes: gidfac41,public X-Google-Thread: f43e6,2c6139ce13be9980 X-Google-Attributes: gidf43e6,public X-Google-Thread: 103376,3d3f20d31be1c33a X-Google-Attributes: gid103376,public X-Google-Thread: 1108a1,2c6139ce13be9980 X-Google-Attributes: gid1108a1,public From: Nick Leaton Subject: Re: Safety-critical development in Ada and Eiffel Date: 1997/08/22 Message-ID: <33FD55E3.CE8A29BF@calfp.co.uk>#1/1 X-Deja-AN: 267862148 References: <33E09CD5.634F@flash.net> <33E9ADE9.4709@flash.net> <5siqrr$3of@jupiter.milkyway.org> <5smgts$p68$1@miranda.gmrc.gecm.com> <33EFCCE4.4CE0@flash.net> <5sskfd$nn5$2@miranda.gmrc.gecm.com> <33F25AA5.49ED@flash.net> <5t1fen$c7d$1@miranda.gmrc.gecm.com> <33F52989.38BB@flash.net> <33F83585.2FB006C3@munich.netsurf.de> <33FA76D7.21D9@flash.net> <33FAB35A.18AA15BB@calfp.co.uk> Reply-To: nickle@pauillac X-NNTP-Posting-Host: calfp.demon.co.uk [158.152.70.168] Newsgroups: comp.object,comp.software-eng,comp.lang.ada,comp.lang.eiffel Date: 1997-08-22T00:00:00+00:00 List-Id: Jon S Anthony wrote: > > In article <33FAB35A.18AA15BB@calfp.co.uk> Nick Leaton writes: > > > > To demonstrate the problem, attempt to encode the critical Ariane 5 > > > assumption as a "top-level abstract class." It is not directly > > > representable > > > as code, even as a "top-level" abstraction. > > > > But neither are any of the specs you have for a fighter > > That's OK, Ken is not the one claiming that this can be done. Meyer > and the E-Jihad are the ones making this fatuous claim. > > > aircraft. Just as you have to decompose your code, you have to > > decompose you assertions or specifications. Just because you can't > > write 'fly plane' and be done with it in Eiffel (or Ada) it doesn't > > make DBC wrong. > > Spoken like a true reductionist. This is not a decomposition problem. > I tried to point this out before when I spoke about how this problem > is the direct analogue of the problem of "natural kinds" in knowlege > representation. You can't come up with contextually independent > necessary and sufficient conditions for a definition for these things. > But that is basically what you are trying to claim _is_ possible. OK, so if you can't write such requirements in a rigorous way, how can you write the application. If you can write an application that meets the requirements, you can write a coded spec for the problem. In the extreme case, the code for the application is the specification. If you cannot code the spec/requirements you can't check that they work. Just because you have a deficient spec, or because you cannot envision what a set of DBC assertions are for a problem doesn't detract from DBC. > > > Said another way, could you write "War and Peace" as a "top-level" > > > abstraction? > > > > Ok. > > > > A hit B and made up. > > Not even close, :-) Unfortunately, it takes up more characters than 'War and Peace' ! -- Nick