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Re: Please advise regarding a design of CIF dictionaries for materialproperties

Dear Nick,

On 10/02/2011 01:18 PM, Nick Spadaccini wrote:

>> x) tags of the same property are split into several loops in data 
>> CIFs?
> I believe your definition of your property is not what you would
> call a category. You CANNOT split tags of the same category across
> loops.

I believe I have found a DDL1 counter-example to the last statement. In
the cif_core.dic, both _atom_site_fract_... and _atom_site_aniso_U_...
data items have category 'atom_site', but they are usually listed in
separate loops, in nearly all CIFs I have seen so far.

> The reason is a loop has to have a key defined. In the REFLN
> category the key is h k l (or [h, k, l] in STAR/DDLm. If you want to
> split the REFLN category across 2 loops, you can have h k l in one,
> then what do you have in the other loop as the key?

The cif_core.dic solves this by declaring _atom_site_label and
_atom_site_aniso_label, and by setting _list_link_parent of
_atom_site_aniso_label (foreign key?) to '_atom_site_label' (primary
key?). The same method could be used in your proposed 'h k l' example,
by declaring _refln_index_xyz_h (foreign keys) as having link parent
_refln_index_h an so forth.


Dr. Saulius Gražulis
Institute of Biotechnology, Graiciuno 8
LT-02241 Vilnius, Lietuva (Lithuania)
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