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Variants

  • To: "Discussion list of the IUCr Committee for the Maintenance of the CIF Standard (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

 _diffrn_radiation_wavelength_
determination

you would add

 _diffrn_radiation_wavelength_variant

and a new variant category


       _variant_variant
       _variant_role
       _variant_timestamp
       _variant_variant_of
       _variant_details

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:

       _variant_variant


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

       _variant_role

             The value of _variant_role  specifies a role

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

       _variant_timestamp


             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.

       _variant_variant_of


             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.

       _variant_details


             A description of special aspects of the variant


An example of how this might be used is:

        loop_
            _diffrn_radiation_wavelength_id
            _diffrn_radiation_wavelength
            _diffrn_radiation_wavelength_determinaton
               1   1.23456   fundamental
               2   1.25      estimated


would become

         loop_
             _diffrn_radiation_wavelength_variant
             _diffrn_radiation_wavelength
                final   1.23456
                pelim   1.25

         loop_
             _variant_variant
             _variant_role
             _variant_timestamp
             _variant_variant_of
             _variant_details
             final preferred 2007-08-04T01:17:28 prelim refined
             prelim .        2007-08-03T23:20:00 . .

         loop_
            _cell_variant
            _cell_length_a
            _cell_length_b
            _cell_length_c
            _cell_angle_alpha
            _cell_angle_beta
            _cell_angle_gamma
            final  22.5 22.5 22.5 90. 90. 90.
            prelim 22.3 22.3 22.3 90. 90. 90.


 Regards,
   Herbert


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

                +1-631-244-3035
                yaya@dowling.edu
=====================================================

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