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do XML Datatypes work for RDF?

From: Dan Connolly <connolly@w3.org>
Date: Wed, 16 Feb 2000 16:18:28 -0600
Message-ID: <38AB2234.D6B9335E@w3.org>
To: www-rdf-interest@w3.org
Short version: the datatypes part of the XML Schema specs
doesn't specify a URI for each primitive type (boolean,
float, double, etc.) but only a URI for all these types.
Is that good enough for RDF use cases?

Details:

The RDF schema WG had an issue(c21) about external type systems;
part of that issue specifically regarded "IEEE floating point numbers,
Integers, Boolean values, Dates and Times, etc". The
issue was deffered, pending an XML-wide solution for such
primitive datatypes. The spec sketches, in example 2, how
this is expected to work:

<rdfs:range
rdf:resource="http://www.datatypes.org/useful_types#FloatZeroToOne"/>
	-- http://www.w3.org/TR/1999/PR-rdf-schema-19990303/

In the XML Schema WG, we're preparing for last call, which
is when we say "all the issues we can find are resolved;
what do you think?" but it's also a time to say "we think
we've met our requirements... do you agree?"

The XML Schema requirement that I proposed to represent
the postponed RDF schema issue turned into:

"The XML schema language must define:

[...]
   3.mechanism for URI reference to standard semantic understanding of a
     construct; "
	-- http://www.w3.org/TR/1999/NOTE-xml-schema-req-19990215#Structural

The WG isn't exactly sure what that means... we agreed in Mar '99 to
clarify it
but we haven't come up with replacement wording since. I was thinking
that it meant we would supply, explicitly, a URI for each of
boolean, float, double, etc. If that's what it means, we haven't met
it. But I need more clear wording to take to the XML Schema WG, along
with use cases, in order to make the case.

I suppose we could use
	http://www.w3.org/TR/1999/WD-xmlschema-2-19991217/#boolean
for the value of the rdf:range property, but that doesn't work
for user-defined derived types.

The schema spec provides an answer of sorts:

"we observe that
[XPointer] provides a mechanism which maps well onto our notion of
symbol spaces.
An fragment identifier of the form
#xpointer(schema/element[@name="person"]) will
uniquely identify the element declaration with name person, and similar
fragment
identifiers can obviously be constructed for the other top-level symbol
spaces."
http://www.w3.org/TR/1999/WD-xmlschema-1-19991217/#ref-schema

Is that good enough?


The schema specs also include:

"RDF Schema 
     XML Schema: Structures has not yet documented requirements or
     dependencies. See [Cambridge Communiqué] for a clarification of the
     relationship between the two, which includes requirements arising
from web
     architecture considerations. "
	http://www.w3.org/TR/1999/WD-xmlschema-1-19991217/#intro-relatedWork

but I don't see anything in the Cambridge Communiqué that's relevant.

The Cambridge Communiqué 
W3C NOTE 7 October 1999 
http://www.w3.org/TR/1999/NOTE-schema-arch-19991007


-- 
Dan Connolly
http://www.w3.org/People/Connolly/
Received on Wednesday, 16 February 2000 17:18:38 GMT

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