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Re: [Cif2-encoding] Splitting of imgCIF and other sub-topics..... .. .

John

> If a CIF processor is presented with a file having no version
> identification comment, then which syntax would you want it to assume?

I'm thinking that's an implementation decision for the author of
that particular CIF processor. Probably most authors should assume
it's a CIF2: as you go on to note, most well-formed CIF1s will be
fully conformant CIF2s.

If the author is sufficiently motivated, he can devise relatively graceful
ways to handle resultant syntax errors (safest is probably to abort but
issue a suggestion that the input file is using a feature no longer
supported; depending on the application, he may provide a switch to process
as a CIF1). If not sufficiently motivated, the input should be handled in
whatever way he has chosen to handle other syntax errors. Declaring a file
to be CIF2 doesn't guarantee it won't have any syntax errors :-)

The latter might well annoy users who don't understand what the problem is,
but an enhanced vcif would, one hopes, be available to help explain what's
gone wrong.

> Making CIF2 accommodate all of CIF1 would require substantial changes
> to those parts of the draft that we have considered settled. Is
> it that important to you?

No, I don't want to revisit those previous discussions. I accept that
formally CIF2 is not 100% backwards compatible with CIF1.

I'm also keen that we encourage the adoption of structured comments as
routine good practice, but I'm reluctant to make them mandatory, largely
for the reason Herbert gave some time ago. If an author sends you a CIF
which is perfectly sound but lacks such a header, and you send it back
demanding one, he will doubtless supply one - but who can say whether
it's credible?

This isn't a game-stopper for me: if we were to vote on this specific
point, I'd say "make it optional", but if the majority view were otherwise,
fair enough. It probably wouldn't stop IUCr from creating in-house
applications that tried to process such "defective" CIFs anyway!

Regards
Brian


On Thu, Sep 16, 2010 at 11:19:13AM -0500, Bollinger, John C wrote:
> Hi Brian,
> 
> On Thursday, September 16, 2010 8:18 AM, you wrote:
> [...]
> >I favour the specification *recommending* a magic string to begin a
> >file: an optional BOM followed by the 11 characters
> >
> >#\#CIF_2.0<whitespace>
> 
> Can you expand on that a bit?  Ignoring all considerations of character encoding, CIF 2.0 syntax is not 100% backwards compatible with CIF 1 syntax.  (Handling of quoted strings is the most prominent area of incompatibility, but there are others.)  If a CIF processor is presented with a file having no version identification comment, then which syntax would you want it to assume?
> 
> [...]
> 
> >These are recommendations, not requirements,
> >
> >1. to include existing CIF1.0 and CIF1.1 instances as valid CIF input
> >streams (whether "decorated" or not;
> 
> Making the version comment optional in CIF2, as you suggest, would make *most* well-formed CIF1 instances also be well-formed CIF2 instances -- but not all of them.  Making CIF2 accommodate all of CIF1 would require substantial changes to those parts of the draft that we have considered settled.  Is it that important to you?
> 
> 
> Thanks,
> 
> John
> --
> John C. Bollinger, Ph.D.
> Department of Structural Biology
> St. Jude Children's Research Hospital
> 
> 
> Email Disclaimer:  www.stjude.org/emaildisclaimer
> 
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