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From: brendan@cs.uq.oz.au (Brendan Mahony)
Newsgroups: comp.specification
Subject: Re: Skepticism Towards Specifications
Message-ID: <1921@uqcspe.cs.uq.oz.au>
Date: 13 Jun 91 01:11:43 GMT
References: <1991Jun12.203347.17380@netcom.COM>
Sender: news@cs.uq.oz.au
Reply-To: brendan@cs.uq.oz.au
Lines: 43

In <1991Jun12.203347.17380@netcom.COM> jls@netcom.COM (Jim Showalter) writes:


>[someone with whom I agree states:]
->I'd assert, however, that
->more than 95% of a reasonably sized program's code is an attempt at writing
->a non-ambiguous specification. 1/2 :-)

It would seem that 5% of the program code is completely wasted then :-).

>I think there is a lesson here for anyone who wants to specify systems
>in a formal language--it may well be the case that any time one wants
>to formally specify a system of suitable complexity to be interesting,
>the resulting specification language is itself so complex that it provides
>scant improvement over English or, alternatively, the language of 
>implementation itself. (There are certainly development groups I'm aware
>of that use Ada as their specification and implementation language.)

I think you are getting a little bit confused between two connotations
of the word specify. I would label them specify-requirements and characterise.
If you want a full characterisation of the behaviour of a program then
it is likely that you will be able to express it most succinctly in the
programming language itself. This is the most complete specification of
the expected behaviour of the program. If on the other hand you simply
want to specify what you intend to use the program to do, it is rare
that arrays, files, pointers, interrupts etc are required to
express your meaning. The best language to write this specification is
the language people normally use in discussing the sort of problem that
is to be solved. If you wish to perform integer calculations then
integer arithmetic proves the appropriate language; if you wish to heat
a room you use the language of thermodynamics; etc.. What you really
need is a specification language that lets you adopt the vocabulary
appropriate to the application domain. It is also useful to adopt a
development strategy that lets you progressively replace the language of
the application domain with the language of programming (arrays, files,
pointers, etc.) so that each level of development may be discussed in
the most appropriate language for the objects being manipulated.

--
Brendan Mahony                   | brendan@batserver.cs.uq.oz       
Department of Computer Science   | heretic: someone who disgrees with you
University of Queensland         | about something neither of you knows
Australia                        | anything about.