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Re: Backus-Naur descriptions for STAR and CIF

  • Subject: Re: Backus-Naur descriptions for STAR and CIF
  • From: "Richard G. Ball" <richard_ball@xxxxxxxxx>
  • Date: Thu, 18 May 2000 14:08:10 +0100 (BST)
On May 17,  8:19pm, Bollinger, John Clayton wrote:
>
> You are missing two things; or actually, two sides of the same thing.
>
> 1) Part of the purpose of BNF is to provide an authoritative
>    description of exactly which constructs are valid "utterances"
>    of the language described.  It is not just a description of how to
>    write a parser for that language that provides the expected
>    answers in a particular software context.
>
[snip]

> It will be clear now that I have come around in my thinking about
> whether a full BNF description of CIF would be desirable.  I definitely
> think it would be.

After reading your comments John and examining the various pathalogical cases
I am coming to the conclusion that ANY reading of a CIF should be done by a
full-blown parser based on a complete BNF descriptor of the "CIF language"
(with whatever changes to the CIF syntax necessary to allow such a descriptor
to be made). Even examining a file to see if there are multiple datablocks
seems to need a complete parsing to ensure the correct extraction of the
block identifiers. Fortunately, given the memory and speed of today's
machines, I don't think this is such an onerous requirement; the CIF can be
parsed in a single pass over the file and all dataitems held in memory to be
supplied to the calling program as and when needed.

Given the above, a fast efficicient parser easily interfaced to a number of
languages and supported by the IUCr does seem the best approach. Such a
parser could be the basis for a CIF-prettifier, a CIF-lint (vcif Mark II ?),
a CIF-editor (edcif ?), CIF-database (dbcif ?), ... :-)

Regards,
Richard


--
Dr R.G. Ball                    |  voice: 732-594-5341
Merck Research Laboratories     |  fax: 732-594-6793 or 6100
PO Box 2000, R50-105            |  email: Richard_Ball@merck.com
Rahway, NJ  07065   USA

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