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Re: CIF formal specification

Brian McMahon wrote:

> While working through final proofs of the Volume G chapter on the CIF
> specification, I have taken the opportunity to address two minor
> problems.
> 
> (1) John Bollinger wrote to me to say:
> 
>>I was going over the specifications for CIF 1.1 currently available from
>>IUCr at http://www.iucr.org/iucr-top/cif/spec/version1.1/cifsyntax.html,
>>and I found a minor inconsistency related to use of the string
>>"global_".  Paragraphs 11, 33, and 57 seem to say that only the string
>>"global_" itself is forbidden as an unquoted data value, whereas
>>paragraph 55 says that string is forbidden as the _start_ of an unquoted
>>data value.  Which is correct?
> 
> 
> global_ in STAR does not take a label, and so its behaviour should be the
> same as loop_ and stop_ (rather than data_ and save_, both of which may be
> expanded with a label). While all these constructs are classified as
> reserved words, the difference in handling the complete and partial words is
> made explicit in para 57 of the syntax document. I have therefore changed
> paragraph (55) to read
> 
> 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 an
>     unquoted string. This is done so that any possible future
>     adoption of STAR features will not invalidate existing CIFs.
> 
> instead of
> 
> 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.

> (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.

> If there are no objections, these changes will be incorporated in
> Volume G.
> 
> Regards
> Brian
> _________________________________________________________________________
> Brian McMahon                                       tel: +44 1244 342878
> Research and Development Officer                    fax: +44 1244 314888
> International Union of Crystallography            e-mail:  bm@iucr.org
> 5 Abbey Square, Chester CH1 2HU, England                   bm@iucr.ac.uk
> _______________________________________________
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-- 
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   John Westbrook, Ph.D.
   Rutgers, The State University of New Jersey
   Department of Chemistry and Chemical Biology
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   e-mail: jwest@rcsb.rutgers.edu
   Ph:  (732) 445-4290  Fax: (732) 445-4320
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