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Re: Specifying values 'less than something' in CIFs?

Dear Saulius,

   The definition of a version of a tag such as


is certainly a possibility, and connecting the value provided
algorithmically in validation with


becomes very feasible in DDLm.  Peter is mistaken about
"CIF is a flat syntax and cannot easy manage complex objects
with facets and attributes".  In imgCIF we handle entire diffraction
images as complex objects.  The question is not about CIF, but
about how you handle complex objects in databases so that the metadata
about the "facets and attributes" becomes searchable.

0.001 is a number. <0.001 is a statement about a range
of numbers.  In CIF at the moment, there is already
a notation for some ranges of numbers, 0.0005(5), for
example, meaning 0.0005+/-0.0005, which may or may not
be intended to convey the same information as <0.001.
mmCIF deals with this complexity by explicitly making
_esd tags.

The issue needs to be dealt with in database searches.
Should a search for .0004 be satisfied by data given
as 0.0005(5)?  Most people would agree.  Should a
search for .0004 be satisfied by data given as <0.001?
Many people would be less certain.   Perhaps it is time to
revisit these conventions and settle on some extensions to the
notation to make life easier for users in preserving essential
metadata compactly while preserving the searchability of data
that includes that metadata.


On 4/29/12 4:16 AM, Saulius Grazulis wrote:
> Dear COMCIF members,
> On 04/29/2012 11:09 AM, Saulius Grazulis wrote:
>> I am currently trying to validate all Crystallography Open Database CIFs
>> against the IUCr core dictionary.
>> A large amount of value type violations come from data items like this:
>> _refine_ls_shift/su_mean<0.001
> It has just occurred to me that we could use _lt data items to covey the
> above message:
> _refine_ls_shift/su_mean_lt 0.001
> This is probably the way how it was meant to be specified, isn't it?
> Sorry for not spotting this possibility before...
> Sincerely yours,
> Saulius

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