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Re: Variants

Dear Joe,

   Once tags have been out and in use for a long time, it is not a good
idea to change them without a strong reason.  Why is id better than

   In real experiments, it is not always intrinsicly clear what is
primary and what is derived.  All you really know is what you in fact
derived from what, i.e., that a given variant is a variant of what
other item, but by the time something gets published, things
may have changed.  For example, you may start with a diffraction
pattern, infer symmetry, work out a cell based on that assumption, refine 
it against the data, look at the cell and its esds, and find yourself
changing the symmetry and redoing the cell.  Once you get the actual
structure and look that thermal parameters, you may change your mind

   I think we have a good change of knowing the tree or cycle of
drivations and what variants we end up preferring, but I am not sure
how to define primary data.


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


On Mon, 30 Nov 2009, Joe Krahn wrote:

> David Brown wrote:
> ...
>> Is a CIF a fixed archive, a place
>> where we entomb a fact of nature, or is it an evolving document that
>> carries it own history along with it?
> CIF is becoming the standard data format for working crystallography
> experiments, not just an archival format. Maybe the goal should be that
> _variant components can be removed from archival CIFs, in a way that
> does not complicate non-variant data.
> To me, the _diffrn_radiation_wavelength_determinaton approach is
> confusing. The wavelength id is defined mainly for multiple wavelength
> experiments. Using _variant, multiple wavelengths might be defined like
> this:
>          loop_
>              _diffrn_radiation_wavelength_id
>              _diffrn_radiation_wavelength_variant
>              _diffrn_radiation_wavelength
>                 1   final   1.23456
>                 1   prelim   1.25
>                 2   final   1.00
> Some suggestions:
> Maybe use "_variant_id" instead of "_variant_variant"?
> Maybe the _variant_* items should include an identifier as to what
> primary value is being varied, when one exists. In this case, the
> wavelength value is the primary varying value, and all others are derived.
> Thanks,
> Joe Krahn
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