RE: A managed phase-out of DDL1 dictionaries
- To: "Discussion list of the IUCr Committee for the Maintenance of the CIFStandard (COMCIFS)" <comcifs@iucr.org>
- Subject: RE: A managed phase-out of DDL1 dictionaries
- From: "Brown, David" <idbrown@mcmaster.ca>
- Date: Mon, 8 May 2017 14:10:13 +0000
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James,
Thanks for the explanation. The idea of a separate subcategory that can be defined sometime in the future when it is needed seems like a satisfactory solution. David I. David Brown
Professor Emeritus Department of Physics and Astronomy McMaster University Hamilton, Ontario, Canada From: comcifs [comcifs-bounces@iucr.org] on behalf of James Hester [jamesrhester@gmail.com]
Sent: May 8, 2017 02:27 To: Discussion list of the IUCr Committee for the Maintenance of the CIF Standard (COMCIFS) Subject: Re: A managed phase-out of DDL1 dictionaries Thanks David for the detailed explanation.
Part of the problem arises because DDL1 allows "both" as a description of the looping behaviour of a dataname. The issues around the need to better describe the meaning of "both" resulted in the '_audit.schema' proposal last year. That proposal allows
items that are not looped in the DDLm core dictionary to become looped in a controlled fashion, and I'd refer any interested parties to the finally approved proposal at
http://comcifs.github.io/looping_proposal.
Given that DDLm forces us to clarify our thinking ("Set" or "Loop", but not "both"), the DDL1 dictionaries can be brought into line by also disallowing "both". Uses of '_list' = 'both' in the cif core dictionary (exptl_crystal_*, publ_author_*, audit_conform_*,
space_group_*) can be inferred to have the meaning "looping is allowed, but if there is only one item you don't have to". Where looping doesn't have carry-over effects on other categories, these can become 'Loop' categories (publ_author, audit_conform). Where
looping does have an effect (multiple space groups mean that multiple cells and multiple sets of atomic positions are also in theory required) we restrict these to 'Set' categories in DDLm and define a new '_audit.schema' to cover the looped situation.
space_group_name_H-M-alt presents an additional issue, as it can be looped even for a single spacegroup, so should be a separate sub-category of space_group and is probably not suitable for the core dictionary in any case as it appears from David's comment
to be of purely theoretical interest. I will adjust the forthcoming revamped DDLm symmetry dictionary accordingly.
I hope it is clear from this that we are not disenfranchising the theoretical community, but simply making sure that we don't stomp on each other's toes.
James.
On 6 May 2017 at 05:31, Brown, David <idbrown@mcmaster.ca> wrote:
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- References:
- A managed phase-out of DDL1 dictionaries (James Hester)
- RE: A managed phase-out of DDL1 dictionaries (Matthew Towler)
- Re: A managed phase-out of DDL1 dictionaries (James Hester)
- RE: A managed phase-out of DDL1 dictionaries (Matthew Towler)
- Re: A managed phase-out of DDL1 dictionaries (James Hester)
- RE: A managed phase-out of DDL1 dictionaries (Brown, David)
- Re: A managed phase-out of DDL1 dictionaries (James Hester)
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