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Re: [ddlm-group] Relationship of CIF2 to legacy platforms

Title:
James asks whether we should require CIF2 to support legacy systems.  I am not sure what James means by 'systems'.  Are these datafiles or programs?  That is to say is the queston 'should CIF2 applications be able to read legacy CIFs?', or 'should legacy CIF1 programs be able to read CIF2 datafiles?'? 

The answer to the first question is definitely 'yes'.  It is part of the mandate of CIF2 that its programs should be able to process the existing archive so that the archive can take advantage of the enhanced functions of DDLm.  The CIF2 dictionaries will alias all the datanames appearing in the CIF1 dictionaries in a way that makes such reading easy.

The answer to the second question is almost certainly no, at least in cases where the CIF data file makes use of the added syntax features.  All the datanames in CIF1.0 dictionaries differ from those in the CIF2 dictionary by not using a period at the end of the category part of the name and in some cases the names differ in other ways.  There would be no point in trying to produce CIF2 compatible CIF1 dictionaries, since the CIF1 dictionaries are poorly designed for maintenance and have poor aliasing features.

David


James Hester wrote: 
Dear All,

I think it would be helpful to make a policy decision regarding our
treatment of legacy systems in CIF2.0.  This concerns first and
foremost Fortran derived line-length constraints, but may impact on
the encoding discussion in deciding which encodings might get some
special treatment.  There may be other such issues as well.
We have a few choices:

1. Disregard legacy system issues when designing CIF2, on the basis
that such systems can continue to use CIF1 and will eventually
disappear at about the same time that it does (sort of like ASCII and
Fortran...)

2. Continue to support legacy systems on the basis that we don't want
to deny such systems the chance to partake of the raw unadulterated
goodness of CIF2, or perhaps more seriously that such legacy systems
are integral to CIF2 takeup.

What do you think?

James.




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