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Re: _atom_site_aniso_label is broken

Apologies for the slow response - as David mentioned, I've been tied up with
knotty hardware problems in the office, as well as being out of the office
at a meeting. I was surprised that Syd had not responded, but it turns out
that he isn't subscribed to this list.

I'm exploring the issue now with Syd, because there is a possible impact on
the way this is explained in Volume G, which is now only days away from
going to press. I hope that one or other of us can report back within a
couple of days once we've analysed the problem and the suggested response in
some detail.

I should say that I think James is doing a valuable service here: the final
form of DDL1.4 was elaborated in the circumstances that David described, but
there never has been, to my knowledge, a proper attempt to implement
software able to validate completely against that specification. Without a
reference implementation, there has always been a possibility - indeed
likelihood - that there were errors.

Herbert is right in claiming that DDL2 comes close to being a normalized
relational database model, and we can be fairly confident that the aspects
of DDL2 that reflect this have been well tested in practice, because the PDB
are running large-scale relational database applications that use them
directly. It's possible, though, that DDL2 retains material imported from
DDL1 to ensure compatibility, but which has never been tested in
implementation and so may also contain errors.

However, it also seems to me that within this group there is support for a
data model that is not that of a normalized relational database - Brian
Toby's arguments strike a sympathetic chord. DDL1.4 distanced itself from
being a complete relational model to accommodate that. In defining a future
development path for DDL applications, COMCIFS needs to consider (helped
greatly by the sort of input that this group is providing here) how
such flexibility can be retained. Personally, I don't discount the
possibility that we may need to continue to support DDL1.4, though
perhaps in the longer term only for a subset of CIF applications. After
all, whatever anyone ould like to see, the established software packages
will continue to pump out large numbers of (ostensibly) DDL1-compliant
CIFs for years to come. For that reason I think it's good to know if DDL1
does offer a fully workable framework for validation, or whether some of 
the attributes it provides are in fact broken The better we understand
why some applications cannot (or should not) conform to a relational
data model, the better placed we will be to determine the best way to
handle them.

Best wishes
Brian
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