Report on activities

[James Hester]

Dear David,

Thanks for bringing me up to date with the ACA discussions.  I'm glad that
you and Ilia are actively dealing with the restraints/constraints
dictionary, and I am concerned that the new symmetry dictionary has bogged
down.  Regarding DDLm, I agree that your efforts are best directed to
actually writing a core dictionary, and the questions that arise in the
process of doing that can be discussed in the DDLm group (as you have been
doing).  I remain optimistic that the detail that we are getting bogged down
in is soon to be resolved.  John W is of course right that the key value of
the dictionaries is in the definitions, although the machine-readable aspect
will become more valuable with the dREL methods.

all the best,
James.

On Wed, Aug 4, 2010 at 1:55 AM, David Brown <idbrown at mcmaster.ca> wrote:

>  Dear James,
>
> I was at the ACA meeting in Chicago last week and I thought it useful to
> bring you up to date on my discusions and plans.  I discussed three
> different dictionary projects with various people.
>
> REstraints/constraints
> Ilia and I picked up earlier on Herbert's suggestion and have already
> drafted an addition to our proposed restraints dictionary.  In addition to
> incorporating Herbert's suggestion, we decided that we would use the
> opportunity to include the possibility of a rigid body restraint as well as
> constraint as this was not possible under our original proposal.  This turns
> out not to be trivial as listing the weighting of the restraint depends on
> how people define the rigid body geometry in their program.  However, in
> discussing problem with various people, including George Sheldrick, it
> appears that a restrained rigid body is generally not considered rigid.
> SHELX makes no provision for anything other than a constraint.  Ilia and I
> will be working through our draft in the light of this discussion and
> submitting our proposal to the core CIF dictionary mainetance group for
> approval.
>
> Magnetic CIF dictinary
> I had discussions with Branton Campbell.  It appears that there has not
> been much progress on the Symmetry-2 dictionary, but Branton was interested
> in adding CIF items for magnetic structure description.  There are problems
> with this that have defeated earlier attempts to define such a dictionary,
> but we may be able to come up with a basic version that could later be
> extended. We are currently exploring this possibility.
>
> DDLm
> I discussed the state of the DDLm project with both Herbert and John
> Westbrook.  The project seems to have gotten bogged down in somewhat (from a
> dictionary point of view) irrelevant detail and Herbert was urging that we
> get a basic dictionary out there, warts and all, and see where the
> weaknesses are when we tackle real problems.  John agreed, but is of the
> opinion that the real strength of CIF lies in the definitions in the
> dictionaries.  We can play around with the syntax as we like, since the
> software can always be changed.  As a result of these discussions I will
> focus my efforts on getting a basic version of the coreCIF dictionary in
> DDLm to Simon and encourage him to experiment with it.  This strategy means
> that I do not need to worry about, e.g., looping methods beyond the level
> that Syd inroduced, and this should speed up getting DDLm cifs into their
> real-time software trials.  Such trials will no doubt reveal problems we
> never dreamed of, and people can continue using regular C(Fs until we are
> ready with a foolproof version of DDLm CIF dictionaries for distribution.
>
> Best wishes
>
> David
>
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>


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