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Re: Another suggestion for the BNF

  • Subject: Re: Another suggestion for the BNF
  • From: "Herbert J. Bernstein" <yaya@xxxxxxxxxxxxxxxxxxxxxxx>
  • Date: Mon, 1 Jul 2002 11:40:34 +0100 (BST)
Dear Nick,

  As a computer scientist, you must be aware that _no_ BNF can fully
and accurate represent a context-sensitive language, such as CIF,
and that users of any BNF for CIF (as opposed to a context-sensitive
set of productions for CIF as we have disccuessed in the past) need
very strong warnings to consult text notes and lexer suggestions
before attempting to understand the BNF or to create a parser.

  Also, as far as I am aware, there is no BNF that has formally been
adopted by COMCIFS are fully and accurately representing CIF.

  I have written Brian and Syd on this matter, and hope you, as
a responsible computer scientist, will join me in urging caution.

  Regards,
    Herbert

Copy of message to Brian:

Dear Brian,

  Are there _any_ BNF's now posted as supposedly representing an agreed
definition of CIF?  If so, this is very dangerous, and damaging to the
future of CIF.  It appears that some people (e.g. Hester) are under the
impression that some of Nick's sketchy and incomplete BNF's are formal,
complete agreed definitions of CIF.  That will result in the creation
of bizarre dialects of CIF (it has already happened at least once).

  Please, if the IUCr site has any BNF posted, please take it down, or at
least post a warning that "no formal BNF for CIF has yet been agreed by
COMCIFS, and those who create parsers from any BNF should be aware, that
since CIF is a context sensitive language, _no_ BNF can possibly be a
complete speficifcation of CIF, and all text notes and lexer suggestions
should be read very carefully in creating a parser from any proposed BNF
of CIF"

  Regards,
    Herbert

=====================================================
 Herbert J. Bernstein, Professor of Computer Science
   Dowling College, Kramer Science Center, KSC 020
        Idle Hour Blvd, Oakdale, NY, 11769

                 +1-631-244-3035
                 yaya@dowling.edu
=====================================================




On Mon, 1 Jul 2002, Nick Spadaccini wrote:

> On Mon, 1 Jul 2002, James Hester wrote:
>
> > Ralf and I have detected what appears to be another problem with the
> > BNF, this time in regard to embedded quotes.   Consider the following
> > bit of text:
> >
> > data_1A4U
> > #
> > _site.id _site.details
> > 'ND'' 'NAD/NADP SELECTIVITY AMINO ACID.'
> > #
>
> > One idea for a fix:
> >
> > <S_quote_string> ::=
> >   { <S_quote> <non_blank_char> | <not_a_S_quote>} * <S_quote> *
>
> Yep that works, and looks like the simplest change.
>
> I will update the BNF shortly - within the hour.
>
> --
> cheers
>
> Nick
>
> --------------------------------
> Dr N. Spadaccini                           Deputy Head of Department
>
> Department of Computer Science &            voice: +(61 8) 9380 3452
> Software Engineering                          fax: +(61 8) 9380 1089
> University of Western Australia            email: nick@cs.uwa.edu.au
> 35 Stirling Highway                      w3: www.cs.uwa.edu.au/~nick
> CRAWLEY, Perth,  WA  6009
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>


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