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Re: Global section in CIF headers

Note that this is not very different in spirit from the existing AUDIT_LINK
category in the Core (see
http://www.iucr.org/__data/iucr/cifdic_html/1/cif_core.dic/Caudit_link.html )

The AUDIT_LINK definition does specify "relationships between data blocks
in the current CIF", but one could extend it to external data blocks as
well. If we were to do that, perhaps a case could be made for an additional
data item _audit_link_block_location that specified a URI of an external
file (or "." for the current file). We had very long discussions ages back
about the dangers of providing such transient locations, but it still seems
the only way that you can usefully do it.

>                        Also, the nature of the relationship could be
> formalised into an enumerated list to help machine-readability.

That's the difficult bit!

Brian McMahon

> Moving on to Brian's suggestion, I think we are overdue for finding a
> way to describe links between data blocks.  However, using a global_
> block to do this restricts the description to a single data file.  As
> an alternative proposal, how about defining a CIF semantic dictionary,
> with the following two datanames in it?
> _semantic.block_id
> _semantic.block_relationship
> These datanames could be looped inside any datablock order to convey a
> series of relationships to other datablocks, including those not in
> the same file e.g.
> loop_
>  _semantic.block_id
>  _semantic.block_relationship
> |Sydney|090909|JRH         'wavelength determination'
> |Sydney|080808|VKP        'identical batch of sample'
> |Sydney|070707|XYZ         'raw powder data'
> |Sydney|060606|ABC        'Lebail refined structure'
> In the example I have used a pd_block.id type construction to uniquely
> identify a datablock.  Also, the nature of the relationship could be
> formalised into an enumerated list to help machine-readability.
Brian McMahon                                       tel: +44 1244 342878
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International Union of Crystallography            e-mail:  bm@iucr.org
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