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Re: [ddlm-group] CIF2 semantics

On null values, I believe "." and "?" are different in meaning from
their unquoted versions, but that unquoted . and ? are both essentially
equivalent null values.

On numbers, past practice has been to treat 4.5 and "4.5" as very
different, the former being a type numb value and the latter being
a type char value.  This was an important and significant early
difference between CIF and STAR and has been used in the handling of
the number-like strings that arise in PDB bib entries, e.g.
1234-5678 is the number 1234e-5678, but "1234-5678" is a string


At 1:24 PM +1000 7/26/11, James Hester wrote:
>Dear DDLm group,
>
>In order to minimise the number of issues we have to discuss in 
>Madrid to clean up CIF2, I would like to turn discussion to those 
>semantic issues which are relevant to the syntax.  I believe that 
>there are three possible types of datavalue: "inapplicable", 
>"unknown" and "string", represented by <full point> (commonly called 
>a "full stop" or "period"), <question mark> and everything else, 
>respectively.
>
>Do we all agree with the following assertion regarding full point 
>and question mark?
>(1) A full point/question mark inside string delimiters is *not* 
>equivalent to an undelimited full point/question mark
>
>Numbers: I believe that strings that could be interpreted as numbers 
>are nevertheless (in a formal sense) just strings in the context of 
>the post-parse abstract data model.  Therefore, whether or not a 
>numerical string is delimited does not change its value: 4.5 and 
>"4.5" are identical values.
>
>Note that this latter assertion does *not* require that 
>CIF-conformant software must always handle numbers as strings; I am 
>making these statements in order to clarify the abstract data model 
>on which the various DDLs and domain dictionaries operate, not to 
>dictate software design.  If your software can manage any potential 
>need to swap between string and number representation of your data 
>value, then more power to you.
>
>Please state whether you agree or disagree with the above. 
>
>James.
>--
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  Herbert J. Bernstein, Professor of Computer Science
    Dowling College, Kramer Science Center, KSC 121
         Idle Hour Blvd, Oakdale, NY, 11769

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                  yaya@dowling.edu
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