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Re: [pdDMG] Revised powder dictionaries for multiple phases

Dear PDDMG,

I am in the process of reviewing the pdCIF chapter for the next edition of Volume G, and have returned to the DDLm version of the powder CIF dictionary. You will recall that the original idea was to have a base dictionary containing all the usual definitions, but maintaining compatibility with core CIF by not adding a phase identifier to the reflection list, and an extension dictionary that extended categories where necessary to account for multiple phases. I am now wondering whether there is any point in splitting the powder dictionary into two parts in this way, as I think that the default approach of powder data software authors is that multiple phases are catered for "out of the box", so the only dictionary that would be used is the extended one.

Are there any objections if I were to reunite the two dictionaries into one document? The only possible issue in software would be those cases where the name of the extended dictionary is used in _audit_conform entries, however the version would be updated to reflect the change so software that pays attention to audit_conform (is there any?) would be safe. Has anybody used the name of the new dictionary in _audit_conform entries?

Thoughts?
James.

On Wed, 9 Nov 2016 at 16:58, James Hester <jamesrhester@gmail.com> wrote:
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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