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DDL Development Subcommittee

	At the Comcifs closed meeting at the Glasgow Congress it was
decided to establish a subcommittee to recommend improvements to the
Dictionary Definition Language (DDL) in order to better serve the
crystallographic community and keep CIF competetive with other application

	As an example of what the future might hold, Syd Hall described a
language that permits a CIF dictionary to include expressions.  This
allows items missing in a CIF to be calculated from items that are
present.  Syd demonstrated a generic program, which, using only
expressions found in the dictionary, could calculate structure factors
from the coordinates found in a CIF.  Our current dictionaries are like
dictionaries that contain only nouns.  By adding expressions we will be
able to include verbs as well, thus bringing CIF one step closer to
natural language.  Syd's demonstration gave us a glimpse of a future in
which standard crystallographic software would be replaced by a generic
interpreter that could translate the expressions in the dictionary into
executable code. 

	The recommendation for a DDL Development Subcommittee arose from a
number of concerns that were expressed at the meeting.  One is that CIF
must remain competetive with other application languages such as XML.  A
second (and equally important) concern is that any new dictionaries must
be compatible with existing dictionaries because of the large investment
that the community already has in them.  Thirdly there is a concern that
by default we are developing two sets of CIF dictionaries, one set written
in DDL1, the other in DDL2.  With protocols being developed that allow the
merging of CIF dictionaries, the existence of two DDLs means that most
dictionaries must be maintained in both forms, giving rise to an
additional overhead that we do not need.

	The meeting agreed to establish a subcommittee with the following
terms of reference: 

 "The DDL Development Committee is responisible for recommending to Comcifs
 changes required in the Dictionary Definition Languages in order to allow
 CIF dictionaries to respond to the changing needs of the crystallographic
 	This charge is phrased in general terms because the committee has a
long-term role, but it was agreed in Glasgow that there were three
particular issues that need to be urgently addressed:
 	1.  The need to resolve the difficulties associated with
 maintaining dictionaries in two different DDLs by developing a version of
 DDL that is upwardly compatible with both DDL1 and DDL2. 
 	2.  The need to remain competitive and compatible with other data
 languages such as XML.
 	3.  The need to incorporate additional functionalities, such 
 as methods, into the DDL. 

	The following have agreed to serve on this subcommittee:

		John Westbrook
		Syd Hall

	We look forward to seeing the proposals they bring forward.

David Brown

Dr.I.David Brown,  Professor Emeritus
Brockhouse Institute for Materials Research, 
McMaster University, Hamilton, Ontario, Canada
Tel: 1-(905)-525-9140 ext 24710
Fax: 1-(905)-521-2773

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