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COMCIFS adopts DDL1

  • To: "Discussion list of the IUCr Committee for the Maintenance of the CIFStandard (COMCIFS)" <comcifs@iucr.org>
  • Subject: COMCIFS adopts DDL1
  • From: David Brown <idbrown@mcmaster.ca>
  • Date: Thu, 01 Dec 2005 15:55:50 -0500
On November 28, 2005  COMCIFS unanimously voted to accept responsibility 
for managing the Dictionary Definition Language 1 (DDL1)

Background
In order to write a CIF one needs to create a dictionary that defines 
the meaning of such items as _cell_length_a  and _atom_site_label.  In 
the early 1990s it was realised that such a CIF dictionary could be 
written using the same syntax as was used for CIFs and this way it would 
be machine readable.  However, in order to write such a CIF dictionary 
one needs to create a second dictionary that defines the properties that 
one would expect a dictionary to supply, e.g., _name, _definition and 
_type (i.e., text or number).  The Dictionary Definition Language was 
conceived to meet this need and a DDL1 dictionary was therefore created 
for use in preparing CIF (and other) dictionaries.

COMCIFS was appointed to created and maintain the CIF dictionaries, but 
maintaining the DDL1 dictionary lay outside its mandate even though no 
other organization had been assigned this responsibility.  This has not 
caused problems since the DDL1 dictionary is relatively simple and there 
has been no need for it to be revised.  Only recently have some minor 
inconsistencies in the DDL1 dictionary been noticed.  These clearly do 
not affect the functioning of the CIF dictionaries or they would have 
been discovered earlier, but they do cause a problem for advanced 
software that uses the DDL1 dictionary to validate itself in the same 
way that a program like enCIFer uses the CIF dictionary to validate a 
CIF.  As we explore the potential of the CIF and DDL standards to 
support advanced software, we find that it is necessary to make changes 
in the DDL1 dictionary.  However, these changes must be agreed upon by 
the community if the integrity of the system is to maintained.  For this 
reason, COMCIFS has decided to adopt DDL1 and appoint a Dictionary 
Management Group for it.  We expect this group to produce a new version 
of DDL1 in which the inconsistencies have been removed.

The present adoption applies only to DDL1 which is used for the core and 
related dictionaries.  It does not apply to DDL2, a somewhat tighter 
dictionary definition language that is used for the mmCIF and related 
dictionaries.

David Brown
Chair of COMCIFS

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