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Re: _atom_site_aniso_label is broken

Hi Brian,

Yes, the timing was a bit unfortunate, especially given that DDL1.4 has
been out there for many years.

> To resolve this error of logic, we shall drop "_list_mandatory yes" from
> the definition of _atom_site_aniso_label that goes out with Volume G (I
> expect to release all the Volume-G compatible dictionaries within the next
> couple of weeks).

There is also the _list_reference problem, whereby _atom_site_aniso_
items have _atom_site_aniso_label as their _list_reference, which would
mean that when _atom_site_aniso items appear in a single loop with
_atom_site_items _atom_site_aniso_label still has to be in the loop.  

> Volume G also contains some discussion of the ATOM_SITE list problem which
> make it clear what the intention is (in just the way elaborated in the
> discussions on this list last week).
> 
> It is too late in the day to make last-minute changes to DDL1.4 definitions
> for release with this Volume - without careful thought and testing there is
> too high a risk of introducing bad side-effects from what appear to be
> sensible modifications. It seems to me that James certainly has the flavour
> of the type of thinking that is needed to interpret the existing
> definitions, and better documentation ought to make the suggested
> procedures explicit, but I think that can only be done when *and if*
> there are functioning reference implementations for full DDL1.4-based
> validators.

Speaking of full DDL1.4 validators, I think I'll have something to show
you in Florence.

There are a number of alternative resolutions to the
_atom_site_aniso_label problem - would it be useful to talk about them
here, or would doing it on the spot (if considered necessary) in
Florence be more effective?

> Florence will provide a great opportunity for the CIF community to consider
> to what extent (if any) DDL1.4 should still be considered "supported",
> and I'm very glad that you will be there, James.

"Un"supporting DDL1.4 is a topic that should provoke plenty of spirited
discussion... is 7 days enough?

See you,
James.
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