Advice on COMCIFS policy regarding compatibility of CIF syntax with other domains

Peter Murray-Rust pm286 at
Thu Mar 10 11:24:17 GMT 2011

On Wed, Mar 9, 2011 at 11:29 PM, Doug <doug.duboulay at> wrote:

> One CIF feature that no other software language supports natively
> are measurement numbers, with their SUs. Maybe they should be encoded as
> tuples for wider compatibility?
> 1.234(45) puts a significant, but not impossible, additional burden on the
programmer. The string is not parsable by mainstream software. There are two
* throw the su away. I suspect most people do this. I have certainly done it
in some cases
* build a data structure that holds it. Our CIFXML and CML do this (and
another opportunity to thank CIF for influencing CML). CIFXML has a "su"
attribute that holds the su value. The software has to work out what the su
value is in absolute (not relative) terms - i.e. the value above is 0.045.
CMLScalar has a range of tools for managing numeric annotation (min, max,
error and errorBasis). It can carry this through a transformation process
that does not change the values (i.e. output what it read in. The CML
software (JUMBO) does not generally do error-proa]pagation though the data
structure is set up to do it.

It's an illustration of how each particular syntactic construct, though
apparently simple, builds up to a level where it becomes unimplementable. A
typical example is the use of \' to add accents. If this is solely
typographic then this is manageable. But suppose I have "\'Ecole". Do I hold
the \'E as
* 1-character (and have to struggle to find the Unicode point)
* 2-character (e-acute codepoint and E)
* 3- character (backslash, ' and E)
and is it different in France and Canada?

The CIF spec does not say how to implement the construct and aalmost
ceryainly different people will use different incompatiable approaches. And
I gave up trying Hungarian diacritics. There is a limit for everyone :-)



Peter Murray-Rust
Reader in Molecular Informatics
Unilever Centre, Dep. Of Chemistry
University of Cambridge
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