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[ddlm-group] THREAD 3: The alphabet of non-delimited strings.

  • To: Group finalising DDLm and associated dictionaries <ddlm-group@iucr.org>
  • Subject: [ddlm-group] THREAD 3: The alphabet of non-delimited strings.
  • From: Nick Spadaccini <nick@csse.uwa.edu.au>
  • Date: Fri, 18 Sep 2009 14:15:50 +0800
  • Authentication-Results: postfix;
As I have written before, non-delimited string (non-DS) that are not of the
Number or Measured types cause problems. Everything you need to include in a
string can be handled by the delimited string types. With the introduction
of compound data structures, restrictions have to be imposed on the allowed
alphabet of non-delimited strings so the scanner is not "fooled".

If you HAVE to use non-delimited strings then the alphabet is restricted to,

non-DS = [A_Za-z0-9./-()+?][A_Za-z0-9_./-()+?]*

(Allowing for / is in deference to James, I don't see a great need for it.)

The square brackets [] are part of the regexp and not allowed characters.
This will cover all numerics including Measured, and decline the first
character as _. None of the token delimiters are included in the alphabet.
Note also the classic example of symop is x,y+1/2,z IS NOT allowed, though a
quick scan of the IUCr cif archive shows many submissions already quite
sensibly use "x,y+1/2,z".

One level of simplification will be in the definition of datanames (DN). We
could simply define a data name as

DN = _{non-DS}

All CIF data names in the new DDLm dictionaries are consistent with this
restriction. A small amount of remediation (which has to be undertaken
anyway) will need to be done for existing domain dictionaries written in
either DDL1 or DDL2.

A further simplification is that one can write the scanner to look for token
terminating characters, rather than DEMANDING it be followed or preceded by
a whitespace.



Associate Professor N. Spadaccini, PhD
School of Computer Science & Software Engineering

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