Report on activities

[David Brown]

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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