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Re: [ddlm-group] Support for legacy files in DDLm
- To: Group finalising DDLm and associated dictionaries <ddlm-group@iucr.org>
- Subject: Re: [ddlm-group] Support for legacy files in DDLm
- From: David Brown <idbrown@mcmaster.ca>
- Date: Fri, 16 Apr 2010 10:41:54 -0400
- In-Reply-To: <r2y279aad2a1004151709t58f6e00l1ac19a15d0b014a6@mail.gmail.com>
- References: <r2y279aad2a1004151709t58f6e00l1ac19a15d0b014a6@mail.gmail.com>
I have checked a typical CIF submission to Acta Cryst. to see if
there are any obvious problems in reading these with a DDLm dictionary
equipped with aliases. The only one I have found so far (and this will
be be very common) is the absence of a list reference in the list of
symops. Originally we assumed they could be indexed according to the
order in which they appear in the CIF and most people still use this
convention. However a list reference has more recently been defined
and is sometimes used. It is char, though for various default reasons
it has more recently been defined as a number. In Syd's poof of
concept dictionary he assumes that it is present (it is requied in
DDLm) and that it is a cardinal number. In those CIFs where the list
reference is explicitly given, it is almost always a number. I have
not seen anything other than a number. To accommodate defaults, in the
latest changes to the CIF(DDL1) dictionary the identity
operation is required to be '1' (which it almost always is). What this means is that reading the symop loop will require the generation of the symop_id in the form of a number if it is not already present. Since the dictionary will require that it be a cardinal number, the parser would presumably have to generate this code if it were not present, and to change it to a number if it were present but not a number (not a common problem). Otherwixe an error warning would be needed. The subsequent manipulation of these numbers should then proceed without problem unless the original CIF carried a non-numeric list reference into the definitions of distnces and angles. In this rare situation the CIF would probably have to be rewritten. In addition to unrolled loops, there may occasionally be some looped items that were never intended to be looped. This might have been adopted to meet a special need, e.g., the description of two different crystal, both of which were used in the experiment. Technically these would be non-conforming and might have to be rewritten. Again these would be rare. David James Hester wrote: I've changed the subject as this requires a separate discussion. |
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