Crystallography Online: the website of the International Union of Crystallography

Hi David,

I support the proposal to establish a group to maintain DDL1. I
nominate Brian to lead the working group.

Regards,

John


David Brown wrote:
> The CIF dictionaries are written using a Dictionary Definition Language 
> (DDL) which is described in a DDL dictionary.  Both the DDL- and 
> CIF-dictionaries use the same DDL and syntax so that is should be 
> possible to read any of the dictionaries using the same software..
> 
> Currently there are two versions of DDL in use.  DDL1 is used for the 
> coreCIF and related dictionaries while DDL2 is used for the mmCIF and 
> related dictionaries.  When these various dictionaries were originally 
> designed it was anticipated that a program designed to validate a CIF 
> could also be used to validate CIF- and DDL-dictionaries.  However, 
> since most of the programming effort has been directed towards the 
> manipulation of CIFs, it is only quite recently that anyone has taken up 
> the challenge of writing software to validate CIF- and DDL-dictionaries 
> against the appropriate version of DDL.  In the course of this work it 
> became apparent that DDL1 contains some errors that make such validation 
> impossible.  The errors are easy to corrected, but there is no 
> individual or organization that has the responsibility for managing DDL1 
> or the authority to approve any changes.  DDL1 is an orphan even though 
> it underpins the whole CIF project.
> 
> DDL1 was written by Hall and Cook (J. Chem. Info. Comp. Sci. (1995) 35, 
> 819-825), but they have moved on and are not interested in managing the 
> earlier versions of DDL.  At the COMCIFS closed meeting in Florence 
> there was general agreement that, because an authoritative definition of 
> DDL1 is essential to the functioning of many of the CIF dictionaries, 
> COMCIFS should take responsibility for its maintenance.  That decision 
> will need to be formally ratified by the voting members of COMCIFS, but 
> before I ask for that vote, I am circulating the proposal to members of 
> the COMCIFS Discussion List for their comment.
> 
> The Florence meeting of COMCIFS also endorsed the idea of moving towards 
> a new (third) version of DDL (star_DDL) that would be compatible with 
> CIF archives written in either DDL1 or DDL2, but that would in addition 
> benefit from what we have learned over the past fifteen years and 
> consequently would result in a much more powerful version of CIF.
> 
> One might ask why it is necessary to patch up DDL1 if it is likely to be 
> superceded by star_DDL.  There are a couple of reasons.  Firstly, there 
> is much work to be done before star_DDL is ready for general use, and 
> dictionaries written using earlier  DDLs will likely continue in use for 
> many years in parallel with star_DDL.  Secondly, the experience gained 
> by developing advanced software for DDL1 will be useful in developing 
> software for star_DDL.
> 
> If you have any comments on this proposal, can you please post them on 
> the COMCIFS Discussion List by Replying to this message during the next 
> four weeks.  After that time I will ask the voting members of COMCIFS to 
> formally adopt the proposal that COMCIFS take responsibility for the 
> management of DDL1.
> 
> David Brown
> Chair of COMCIFS
> 
> 
> ------------------------------------------------------------------------
> 
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> comcifs at iucr.org
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   John Westbrook, Ph.D.
   Rutgers, The State University of New Jersey
   Department of Chemistry and Chemical Biology
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