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Discussion paper on allowing redefinition of datanames in CIF

  • To: "Discussion list of the IUCr Committee for the Maintenance of the CIFStandard (COMCIFS)" <comcifs@iucr.org>
  • Subject: Discussion paper on allowing redefinition of datanames in CIF
  • From: James Hester <jamesrhester@gmail.com>
  • Date: Fri, 9 Dec 2016 15:38:49 +1100
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Dear COMCIFS,

In the process of preparing the DDLm version of the modulated structures dictionary, it came to my attention that this dictionary nowhere defines a dataname to hold the new model structure factor.  This turns out to lead to a more fundamental issue involving most dictionaries, and requires some sort of resolution from this group. I have written a discussion paper to get us started which I've placed at 
https://github.com/COMCIFS/comcifs.github.io/blob/master/changing_meanings_discussion_paper.md

The key proposal is to allow dictionaries to redefine datanames as long as the old meaning can be viewed as a special case of the new meaning. A new dataname to flag redefinitions is included.

It would be great if any of you with an interest in describing experiments not covered by core CIF (magnetism, modulation, twinning, multipole, polarisation, powder, electron microscopy,...) could consider these issues and provide feedback, corrections and improvements.  Note that this is not particularly CIF-specific.

Once the opinion of this group is clear, we can delegate the detailed work to the DDLm-group after which a formal proposal would return here for approval.

James.
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