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Re: Another suggestion for the BNF

  • Subject: Re: Another suggestion for the BNF
  • From: Brian McMahon <bm@xxxxxxxx>
  • Date: Mon, 1 Jul 2002 13:42:58 +0100 (BST)
Herbert is correct that there is not yet an "official" specification for CIF
syntax incorporating a BNF, although COMCIFS has been working towards such a
reference document for some time and has an advanced draft in hand.

However, so long as it is understood that a BNF representation is necessarily
incomplete, I rather welcome this round of discussion, both because it helps
resolve errors or ambiguities in the current draft and because it is an
excellent example of community cooperation in working towards a common
understanding of the standard and guarding against the proliferation of


On Mon, Jul 01, 2002 at 11:40:34AM +0100, Herbert J. Bernstein wrote:
> 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
> =====================================================

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