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  • To: "Discussion list of the IUCr Committee for the Maintenance of the CIFStandard (COMCIFS)" <comcifs@iucr.org>
  • Subject: Variants
  • From: James Hester <jamesrhester@gmail.com>
  • Date: Thu, 26 Nov 2009 10:59:19 +1100
I'm reposting Herbert's message in a new thread to aid organisation.  Herbert wrote:

Dear Colleagues,

 While you are revisiting this item, I would suggest you consider the more complete (and, I believe, more elegant and general) solution of defining "variants", that we have introduced into the imgCIF dictionary to handled quantities that may be determined in different ways.

 Instead of adding


you would add


and a new variant category


which would allow you with complete generality to manage any number
a refined or redefined quantities, such as wavelengths.  This would
then allow you to us the same variant identifier, for, say cell
dimensions, which could be expected to change in a coupled manner
with the changes in wavelength.

 If you are interested in this more complete approach, I can provide
you with the full item definitions, but the short form is:


             The value of _variant_variant must uniquely identify
             each variant for the given diffraction experiment and/or


             The value of _variant_role  specifies a role

             for this variant.  Possible roles are null, "preferred",
             "raw data", and "unsuccessful trial".


             The date and time identifying a variant.  This is not
             necessarily the precise time of the measurement or
             calculation of the individual related data items, but a timestamp that
             reflects the order in which the variants were defined.


             The value of _variant.variant_of gives the variant
             from which this variant was derived.  If this value is not
             given, the variant is assumed to be derived from the default
             null variant.


             A description of special aspects of the variant

An example of how this might be used is:

               1   1.23456   fundamental
               2   1.25      estimated

would become

                final   1.23456
                pelim   1.25

             final preferred 2007-08-04T01:17:28 prelim refined
             prelim .        2007-08-03T23:20:00 . .

            final  22.5 22.5 22.5 90. 90. 90.
            prelim 22.3 22.3 22.3 90. 90. 90.


 Herbert J. Bernstein, Professor of Computer Science
  Dowling College, Kramer Science Center, KSC 121
       Idle Hour Blvd, Oakdale, NY, 11769


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