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From: anthony@cs.uq.oz.au (Anthony Lee)
Newsgroups: comp.software-eng
Subject: Re: Modifiability
Message-ID: <1849@uqcspe.cs.uq.oz.au>
Date: 9 Jun 91 10:23:45 GMT
References: <1991Jun5.201807.13286@netcom.COM> <62683@siemens.siemens.com> <11714@ncar.ucar.edu> <1991Jun7.165928.1903@weyrich.UUCP>
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In <1991Jun7.165928.1903@weyrich.UUCP> orville@weyrich.UUCP (Orville R. Weyrich) writes:

>>Balzer, Cheatham and Green in their classic paper 'Software Technology in the
>>1990's: Using a New Paradigm' (IEEE Comp. Nov 1983)  proposed that a program's
>>specification be formalized and that the implementation be mostly automated. 
>>The problem then of maintainability would be pushed into the specification
>>phase.

>The problem with this is that the specification becomes to all intents and
>purposes the programming language, and if Ada or C (or something else) is
>later generated automatically from this specification, its just an intermediate
>pass of a huge compiler.

>In effect, the specification language becomes the language in which the 
>source code is written.

I disagree, there are two problems with trying modify a software from a 
natural language specification.

1. The specification is most likely to be ambigious and the 
designer of the modification has to make the best **guess**.

2. It is very difficult for the designer of the modification
to figure out the effect of his modification on the existing
software.  Formal specification is more than just a higher level
programming language.  It allows the designer of the modification
to reason about the effects of his modification on the rest of
the system.

Furthermore you have to consider that the modification could have
taken place several months after the delivery of the original
product (or even years).  How can you guarantee that the source 
code of the original product would be available.  

Even if the source code was availabe it far more difficult to analysis
for conflicting properties between existing software and new software
at the source level.

--
Anthony Lee (Michaelangelo teenage mutant ninja turtle) (Time Lord Doctor) 
email: anthony@cs.uq.oz.au			    TEL:+(61)-7-365-2697 (w)
SNAIL: Dept Comp. Science, University of Qld, St Lucia, Qld 4072, Australia