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RE: A managed phase-out of DDL1 dictionaries

Thanks for the more detailed explanation.  I agree with seeing what the state of
 the community is in two years rather than deciding now.

I remain slightly worried about the DDLm matching changes to DDL1 – as code that
 reads historic CIF already has to cope with quite a few different ways of speci
fying space groups (for example) and adding further improved methods will increa
se complexity.  We may reach a point where parsing a CIF is simple, but writing
code that will reliably interpret what is intended by the values in a majority o
f extant CIF requires quite a steep learning curve involving many previous versi
ons of the dictionaries.

I am interested in understanding the benefits in back porting DDLm changes to DD
L1, and the trade-off of these against the cost of change.  What I am wondering
is whether it would be better to have DDL1 remain as-is, and keep the better rep
resentations only in DDLm; the advantage being that if DDLm support is being add
ed to existing code, then that would also be a good point to add support for imp
rovements in semantics.  Back porting to DDL1 risks imposes an otherwise unrelat
ed change ahead of the need to add DDLm support, which might actually detract fr
om the effort required to add DDLm support.

Best wishes,


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