# 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:

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

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_

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2009-09-25 Proposal from the Nick Spadaccini on the COMCIFS dicsussion list to replace a withdrawn proposal.

_type                        char
_list                        both
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 wrote:

=====================================================
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.

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_
1   1.23456   fundamental
2   1.25      estimated

would become

loop_
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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