Why XML data typing is hard

[W. Eliot Kimber]

At 09:43 AM 11/30/98 -0500, david at megginson.com wrote:
>Michael Kay writes:
>
> > "4,50" is a localized rendition of a float value. But in XML we
> > should encourage a rendition-independent encoding of information.
>
>That is one of the biggest problems with applying concepts from data
>storage to syntax.  XML *is* pure external representation -- in a
>database, I can take any of the following appropriate to my locale and
>store it internally as the same bunch of bits:

I observe that in the SGML Extended Facilities (part of ISO/IEC
10744:1997), we expressly defined a mechanism for *lexical* typing of
attributes and content, although our original idea was to define a
mechanism for *data* typing. This is because we realized that at the syntax
level all we can talk about meaningfully is spelling rules, not semantic
rules.

In the Web SGML TC, we have added the ability to associate notations with
particular attributes, to indicate that the interpretation of the value is
governed by a particular notation. This is one way to get data typing, that
is, the translation of a particular syntactic expression into a semantic
object.

Cheers,

E.
--
<Address HyTime=bibloc>
W. Eliot Kimber, Senior Consulting SGML Engineer
ISOGEN International Corp.
2200 N. Lamar St., Suite 230, Dallas, TX 75202.  214.953.0004
www.isogen.com
</Address>

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