Status of updated version of DDLm core cif

[James Hester]

Dear Core Dictionary Maintenance Group,

The 6-week review of the DDLm version of the core dictionary has ended.
However, serious discussion is continuing in the DDLm group (see messages
following from
http://www.iucr.org/__data/iucr/lists/ddlm-group/msg01428.html and
subsequent threads) around a way to allow looping of ordinarily
single-valued datanames.  That discussion arose from a need to resolve the
schizophrenic nature of the symmetry dictionary datanames: they are
loopable, but are aliased to the old 'unloopable' symmetry datanames, and
are indeed almost exclusively assumed to be unlooped in current software;
for more details see that discussion thread.

While undesirable, it is just possible that, as a result of these
discussions, the DDLm core dictionary may need some minor changes. If any
changes involve a changed dataname or interpretation of a dataname, the
changed portions will be presented here for your review.

In any case, I will hold off passing the DDLm core_cif dictionary to
COMCIFS for final approval until the discussions in the DDLm group have
been resolved, so I continue to invite any further comments that you have
on the current version.

best wishes,
James Hester
Acting Core DMG chair



On 13 May 2016 at 12:22, James Hester <jamesrhester at gmail.com> wrote:

> Dear Core CIF DMG members,
>
> I have completed merging the symmetry dictionary into the draft DDLm core
> CIF dictionary with advice from David Brown. To avoid cluttering your
> mailboxes with 1M files, the link to the latest version is:
>
> https://github.com/COMCIFS/cif_core/blob/cif2-conversion/cif_core.dic
>
> Unfortunately there are too many changes for the Github automated 'diff'
> listing of the changes to be provided. The important changes can all be
> found following the 'SPACE GROUP' category, and see my notes below.
>
> A new 6-week review period starts today.  As before, please check those
> areas of the dictionary that time and your expertise permit, and start a
> new mail thread for each distinct topic to help manage the conversation.
> Even if you find no issues, a public message that you have conducted a
> review and are satisfied is better than silence.
>
> James Hester (acting Core DMG chair).
>
>
> Notes on the symmetry dictionary merging:
> ==================================
>
> (1) Categories 'symmetry' and 'symmetry_equiv' have been changed to
> 'space_group' and 'space_group_symop' respectively, in line with the names
> used in the symmetry, modulated structures, and forthcoming magnetic
> dictionaries.
> (1.1) Where the part of the name following the category name differs, the
> symmetry dictionary version was chosen.
> (2) Category 'space_group_Wyckoff' has been transferred across from the
> symmetry dictionary
> (3) New category 'space_group_generator' has been created as the space
> group generators should not be looped together with the symmetry operators.
> (4) Category 'space_group' is now not loopable, that is, only a single
> space group can be provided in any data block (as was the case for the
> 'symmetry' category). If this wrecks your use case, please start a
> conversation.
> (4.1) Any datanames used to identify a particular space group from the
> loop of space groups have therefore been dropped as they are now unnecessary
> (5) Datanames from the symmetry dictionary linked to the reference setting
> have not been merged as, to be useful, they would require new datanames for
> every affected concept e.g. atom_site.pos_x_reference, refln.hkl_reference.
> These would only clutter up the core dictionary but might be usefully
> defined in a reborn symmetry dictionary if anyone wants to volunteer.
>
> --
> T +61 (02) 9717 9907
> F +61 (02) 9717 3145
> M +61 (04) 0249 4148
>



-- 
T +61 (02) 9717 9907
F +61 (02) 9717 3145
M +61 (04) 0249 4148
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