Request for discussion: dual-version CIF conformance

James Hester jamesrhester at gmail.com
Wed Jul 19 14:16:00 BST 2017


I believe that John's analysis is correct.

On 19 July 2017 at 06:15, Bollinger, John C <John.Bollinger at stjude.org>
wrote:

> Dear Colleagues,
>
>
>
> I have lately been scrutinizing the CIF 1.1 specifications in ITvG and
> carefully considering a variety of unusual cases.  One of the less obscure
> questions I have examined in the course of this process is whether a CIF
> can simultaneously comply with both CIF 1.1 and CIF 2.0.  Up to now I have
> supposed that CIF 2.0’s requirement for a leading version-identifying
> comment prevents a file conforming to CIF 2.0 from also conforming to CIF
> 1.1, but I am having trouble supporting that with the letter of the CIF 1.1
> specifications.  In particular,
>
>
>
> - momentarily disregarding the question of version-identification
> comments, there is, in fact, a common subset of CIF 1.1 and CIF 2.0
> syntaxes on those systems where local text conventions line up with CIF
> 2.0’s encoding and line-termination requirements.
>
> - CIF 1.1 does not require a version-identification comment to appear at
> all.
>
> - Although CIF 1.1 defines a format for a version comment that claims
> conformance with CIF 1.1, it does not specify that files claiming
> conformance to a different version thereby fail to conform to CIF 1.1.
>
> - In fact, the text seems to suppose that a file may conform to multiple
> CIF versions, for it remarks that “A CIF may be considered compliant
> against the most recent version for which it in practice it satisfies all
> syntactic and content rules […],” and it characterizes the version comment
> as embodying only a creation-time conformance assertion.
>
> - If it were necessary, a version comment specifying CIF 2.0 could be
> interpreted as a plain comment in CIF 1.1.
>
>
>
> Does anyone want to mount a counterargument?  Or am I maybe late to this
> party?
>
>
>
> As a concrete example, consider a machine whose text conventions rely on
> an ASCII-compatible encoding and use a line feed character as a line
> terminator (maybe some flavor of Linux).  If the following text is recorded
> on that machine in a file complying with its text conventions, then does
> the file simultaneously conform with both CIF 1.1 and CIF 2.0?
>
>
>
> #\#CIF_2.0
>
> data_example
>
> _item value
>
> ### end of CIF ###
>
>
>
> Note that this is a different question from whether a processor that
> supports only CIF 1.1 should assume that it can handle such a file.
>
>
>
>
>
> Regards,
>
>
>
> John
>
>
>
> --
>
> John C. Bollinger, Ph.D.
>
> Computing and X-Ray Scientist
>
> Department of Structural Biology
>
> St. Jude Children's Research Hospital
>
> John.Bollinger at StJude.org
>
> (901) 595-3166 [office]
>
> www.stjude.org
>
>
>
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