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Re: NOTATIONS and DATA TYPES (was: Update on namespaces)

From: Joe English <jenglish@crl.com>
Date: Wed, 11 Jun 1997 13:32:19 -0700
Message-Id: <199706112032.AA06422@crl2.crl.com>
To: w3c-sgml-wg@w3.org

Andrew Layman <andrewl@microsoft.com> wrote:
>
> My understanding on notations is that the ExternalId used refers to some
> processor capable of interpreting the data (e.g. a program that can read
> and display GIF bitmaps if the external binary resource is in fact a GIF
> bitmap).  Do I read this correctly?

That was the original intent as I understand it,
but I've never seen <!NOTATION...> actually used that way,
and it would make very little sense to do so, at least 
for general SGML.

The idea that there is *one* application capable of doing all
possible processing on a data entity, and moreover that the
location of that application should be hardwired into the DTD,
is in direct contradiction to the principles of data reuse and
system independence.

The situation might be different for XML; since we're assuming
a Web-based environment it *might* make sense to specify the URI 
of a Java applet -- all that's missing is an API with which
the applet can interact with the application -- but that would
leave Perl, Python, Tcl, et cetera-based XML processors out of
the picture.  IMO Internet Media Types (MIME types) would make
much more sense as notations' SYSTEM identifiers in XML.


> If my understanding of NOTATION is correct (from section 4.6 in the
> working draft at
> http://www.textuality.com/sgml-erb/WD-xml-lang.html#sec4.6), then a
> NOTATION in effect says "I don't know how to deal with this external
> resource, but here is the identifier of some processor that does."  Data
> types would be saying "This is a number (date, time, etc.) I make no
> recommendations regarding processing."


The XML draft does lend itself to that interpretation.
In full SGML though -- where NOTATIONs can be associated with
external CDATA entities (which XML lacks) and elements --
they are often used to indicate data types in the sense
you describe.


--Joe English

  jenglish@crl.com
Received on Wednesday, 11 June 1997 16:35:41 EDT

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