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Re: A formal specification for CIF version 1.1 (Draft)

  • Subject: Re: A formal specification for CIF version 1.1 (Draft)
  • From: Brian McMahon <bm@xxxxxxxx>
  • Date: Thu, 11 Jul 2002 11:00:18 +0100 (BST)
Dear John

Thanks for your careful reading of the spec and your many comments. Herbert
is doing a good job of providing responses to points of detail. I want to
make the general point that most of the things you single out are indeed
intended as clarifications and not novel features. And the clarifications
are indeed needed, for no two parsers that I have tested have understood the 
syntax identically. As you note, vcif, which I have used for many years
as a reference syntax checker (and which was written specifically for that
purpose) is at variance with some of the specific points of clarification,
and will itself need to be corrected if this document is accepted as 
stands.

However, I also point out that most of the cases are indeed what you call
"corner cases". While it is important that reference parsers exist, in
practice many CIF applications will be built that are very robust yet
ultimately fail one or two of the trip tests - and a pragmatic approach to
that could be the development of a CIF normaliser that can trap and handle
the more esoteric deviations in a preprocessor stage.

I have to say that I have seen more broken CIFs with gross errors that a
casual reading of the original paper should have caught than I have CIFs
that are subtly wrong through misinterpretation of the fine points
elaborated in this spec document.

One point to note. The extension involving introduction of square brackets 
is not just an extension to CIF; it requires a formal extension to the
STAR format. So far as I am aware, this extension (arising from some very
nice work Syd and Nick have done on dynamic generation of STAR data from
related values) has not been formally published. A public extension of
STAR is necessary before COMCIFS can formally adopt CIF 1.1 as it stands.

Cheers
Brian

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