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Re: CIF formal specification

Hi John and other comcifers.

>> 55. The reserved word global_ (in a case insensitive     form). This 
>> is actually a reserved word of STAR, but is defined
>>     here so that it may be explicitly excluded as THE START OF an
>>     unquoted string. This is done so that any possible future
>>     adoption of STAR features will not invalidate existing CIFs.
>
> I thought the use of global_ had been deprecated.  It has no
> correspondence in ddl2 applications and I would prefer to see this
> just die a quiet death.

global_ has certainly not been deprecated in the STAR file syntax and
is unlikely to be; being extremely useful for some applications. I
believe the wording of 55. points this out correctly and I support
its reservation for future CIF considerations.

>
>> (2) Peter Murray-Rust told me that the formal specs do not actually
>> state explicitly that the order of data names is irrelevant. I have
>> addressed this by adding the text in capitals to para (7):
>> 7. A given data name (tag) (see 2.4
>>    and 2.7) may appear no more than once in a given data block or
>>    save frame. THERE IS NO SIGNIFICANCE TO THE ORDERING OF DATA NAMES
>>    WITHIN A DATA BLOCK OR SAVE FRAME. THAT IS, A DATA NAME WITH ITS
>>    ASSOCIATED DATA VALUE OR SET OF DATA VALUES MAY BE RELOCATED WITHIN
>>    THE SAME DATA BLOCK OR SAVE FRAME WITHOUT CHANGING THE 
>> INTERPRETATION
>>    OF THE DATA. A tag may be followed by a single value, or a list of 
>> one
>>    or more tags may be marked by the preceding reserved 
>> case-insensitive
>>    word loop_ as the headings of the columns of a table of
>>    values. White space is used to separate a data block or save frame
>>    header from the contents of the data block or save frame, and to
>>    separate tags, values and the reserved word loop_
> Ordering does have some implications.  While the order of categories is
> of no importance, data items within categories must be collected
> together at one point in each data block.  The repetition of a category
> section in mmCIF is both a logical and syntax error.

I believe that John's comment about ordering refers specifically to data
items in a looped list. Clearly in this case data items in a given 
category
MUST be together (though the order within that list should not be 
relevant)
because the category key item(s) CANNOT be replicated in another looped
list. A looped list may contain only items of the same category. As far 
as
I am aware there is no ordering constraint on data items that are not 
in a
list... and indeed if there were, I suspect that many of the archived 
CIFs
for Acta, and elsewhere, would be non-compliant! Provided that a CIF 
parser
maps data items in a file back to the relevant dictionary I don't see 
that
the category identity is a problem.

Cheers
Syd
------
Professor Sydney R. Hall
School Biomedical & Chemical Sciences
University of Western Australia
Crawley, 6009  AUSTRALIA.
Ph: +61 (8) 6488 2725
Fx: +61 (8) 6488 1118
"Data data everywhere but not a thought to think!" - Theodore Roszak

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