Re: [xml-dev] The meaning of the "string" datatype?

[Rick Jelliffe <rjelliffe@allette.com.au>]

Costello, Roger L. wrote:
>  
> The content of <Author> can be characters from any language - English, Chinese, Arabic, Italian, Greek, German, Spanish, Russian, etc - plus punctuation symbols plus math symbols. If I did my arithmetic correctly [1], the total number of different characters is: 1,112,000.
>   
Strictly, languages don't have characters, they have writing systems, 
and writing systems use scripts, and scripts are made from characters.

Furthermore, Unicode has Private Use Areas which allow non-standard 
characters to be represented.

XML Schemas String datatype is perhaps better thought of as an 
anti-datatype rather than a datatype. What it does is signify an absence 
of a value-space: it is not asserted to be a number, not asserted to be 
a date, not asserted to be a boolean. 

This is of course a little topsy turvy. I had a case with an insurance 
company who received data from the agents which had standard fields but 
the fields could contain any notation. There was a separate process 
where people would check the fields and "re-work" them into the standard 
notations. So the input might have
  <date>20th May, 2010</date>
and after rework it would contain
  <date>2010-05-20</date>

They were surprised to learn that they could not merely say that the 
incoming data was a string, and then restrict this string to be a date 
type. (Since xs:date is not a restriction of xs:string.) The original 
XML Schemas datatype hierarchy was not designed with document refinement 
in mind (i.e. marking up the document, passing it as text through 
several different XML stages): the design only makes sense if you assume 
that the data is living in a DBMS, i.e. where the types are actually 
primitive storage types for DBMS.

Cheers
Rick Jelliffe