[pdDMG] DDLm version of Powder CIF dictionary

[James Hester]

Dear Powder Diffraction Dictionary Management group members,

Last year at the Monreal IUCr meeting, COMCIFS decided that all DDL1 CIF
dictionaries would be rewritten in the new dictionary language DDLm.  A
draft version of a DDLm powder dictionary is now available for perusal at
https://github.com/COMCIFS/cif_core/blob/cif2-conversion/cif_pow.dic  A
brief guide to reading DDLm dictionaries is available at
http://www.iucr.org/resources/cif/ddl/ddlm/docs/intro

A friendlier auto-generated HTML version of the powder dictionary with
definitions and aliases only is available at
http://comcifs.github.io/cif_pow.dic.html

As you will probably remember (although the last message to the group was
over a decade ago and the dictionary itself is almost 20 years old) the
powder dictionary presents some unique problems, in that powder instruments
come in a variety of geometries and powder data/results may be tabulated in
a variety of ways.  In performing the conversion, I have endeavoured to
preserve the original meanings, while nevertheless conforming to the more
precise DDLm framework.   The implications of this dictionary for the
working powder diffraction programmer should ideally be as follows:
(1) authors of CIF writing software: none - the original datanames are
aliased to the new datanames, so can be used without change in keeping with
the general principle that we cannot change the meaning of datanames.
(2) authors of CIF reading software: a complete new set of datanames where
a period character "." replaces an underscore and an underscore replaces
"/" are defined. In all cases, replacing any "." and "/" characters in a
dataname with underscores will yield a 'normalised' dataname that is
guaranteed to be unique.

I did encounter a few issues that the pdDMG will need to resolve, which I
will post in separate threads to make discussion easier (see
https://github.com/COMCIFS/cif_core/issues if you can't wait).

James Hester.
(COMCIFS chair)
-- 
T +61 (02) 9717 9907
F +61 (02) 9717 3145
M +61 (04) 0249 4148
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