[pdDMG] Revised powder dictionaries for multiple phases

[James Hester]

Dear PDDMG,

I have now created a draft DDLm powder 'multiphase' dictionary to reflect
the discussion on multiple phases. Please look at
http://comcifs.github.io/cif_pow_multiphase.dic.html for an HTML version,
or
https://github.com/COMCIFS/cif_core/blob/cif2-conversion/cif_pow_multiphase.dic
for the text version. This dictionary contains only 4 dataname definitions,
for the _pd_phase datanames and for pd_refln.phase_id.  I have made the
somewhat arbitrary decision that _pd_phase.mass_percent is not necessary
for a single-phase sample (happy to move it back to the main dictionary if
there is disagreement on this).  cif_pow has been updated accordingly,
accessible from the links that I sent previously.

As written, if any phases are presented in separate datablocks (and this is
the only way to present multiple phases) then this extension dictionary
will apply and the datablock should have '_audit.schema' set to
'Multiphase'.

The way that this works together with the cif_pow dictionary and cif_core
dictionary is that the cif_pow_multiphase dictionary is the 'master'
dictionary which imports all of the definitions in cif_pow and cif_core,
and then (i) overrides the definition for the REFLN category in cif_core to
add '_pd_refln.phase_id' as a key column and (ii) overrides the definition
for PD_PHASE in cif_pow to make it a Loop category (i.e. multiple phases)
with key '_pd_phase.id'.

In essence, once this scheme is accepted, if you wish to output phases in
separate datablocks then the 'master' datablock should have '_audit.schema'
set to 'Multiphase'.  No other changes to the way things have been done for
DDL1 should be necessary.

If you reply to this message, please cc me as there appears to have been
some issues with the listserver at the IUCr.

James.


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