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Re: Variants

I include David's original message below for reference.

---------------------------
(from David Brown)
Dear Colleagues,

Last September I circulated for fast track approvel a recommendation for adding a new item:                         
    

                 _diffrn_radiation_wavelength_nominal,

to the core dictionary (see below for details).  The intent was that this could be used for giving a nominal wavelength calculated e.g., from the paparmeters of a diffractometer.  It was proposed tht this might be needed for completeness even though it was not accurate enough for calculating  lattice parameters, etc.  This proposal was passed by the core CIR dictionary maintenance group by default (no one raised any objection).  When this proposal was subsequently presented for final approval to COMCIFS, Nick Spadaccini suggested a more elegant alternative, namely that by adding instead the item

        _diffrn_radiation_wavelength_determination 

we could loop the nomiinal wavelength with the  refined (and any other interesting) wavelengths.  This would be more informative and allow for future expansion.

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

According to our rules, this proposal is being posted for comment to the coreCIF dictionary maintenance group for the next six weeks.  At the end of this time, if there are no unresolved issues, the core dictionary maintenance group will be deemed to have accepted the proposal.

David Brown

==============================================================

The proposal is to add the following item to the coreCIF dictionary:
=============================================
2009-09-25 Proposal from the Nick Spadaccini on the COMCIFS dicsussion list to replace a withdrawn proposal.

data_diffrn_radiation_wavelength_determination
  _name                      '_diffrn_radiation_wavelength_determination'
  _category                    diffrn_radiation_wavelength
  _type                        char
  _list                        both
  _list_reference            '_diffrn_radiation_wavelength_id'
 loop_
   _enumeration
   _enumeration_detail
  'fundamental'           
       'Wavelength that is a fundamental property of matter e.g. MoK\alpha'
  'estimated'               
       'Estimated from secondary information e.g. monochromator angle or time of flight'
  'refined'                 
       'Based on refinement using a standard material with known cell parameters'


  _definition
;              The method of determination of incident wavelength. Further information may be provided in _diffrn_radiation_special_details
;


On Thu, Nov 26, 2009 at 1:14 PM, Herbert J. Bernstein <yaya@bernstein-plus-sons.com> wrote:
You removed David's original message from mine.  Please add that to
the thread as well.


=====================================================
 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
=====================================================

On Thu, 26 Nov 2009, James Hester wrote:

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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