Re: Report on activities

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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