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[Fwd: Re: CURIEs, xmlns and bandwidth]

From: Pete Johnston <p.johnston@ukoln.ac.uk>
Date: Fri, 04 Nov 2005 16:01:57 +0000
Message-ID: <436B85F5.8080108@ukoln.ac.uk>
To: public-rdf-in-xhtml-tf <public-rdf-in-xhtml-tf@w3.org>

I tried to post the message below earlier but it doesn't seem to have
got through to the list.

I think Mark's last message [1] is saying that - contrary to my
assumption below - the value space of CURIE is indeed a set of
{namespace name, local part} pairs, not a set of URIs.

But it might help the discussion if this is clarified?

Cheers

Pete

[1]
http://lists.w3.org/Archives/Public/public-rdf-in-xhtml-tf/2005Nov/0011.html

-------- Original Message --------
Subject: Re: CURIEs, xmlns and bandwidth
Date: Fri, 4 Nov 2005 09:21:07 +0000
From: Pete Johnston <p.johnston@ukoln.ac.uk>
To: Ben Adida <ben@mit.edu>
CC: Norman Walsh <Norman.Walsh@sun.com>, public-rdf-in-xhtml-tf@w3.org,
iptc-metadata@yahoogroups.com
References:
<A29ADE959C70A1449470AA9A212F5D808B3354@LONSMSXM06.emea.ime.reuters.com>
<87wtjp777t.fsf@nwalsh.com> <8A3840A2-10FD-4168-892E-C84EC7205596@mit.edu>

Quoting Ben Adida <ben@mit.edu>:

> I want to stress again that we should not confuse issues here. 
> Conceptually, CURIEs are meant to be very similar to QNames. The only
>  goal is to allow for the expression of *any* URI in a compact way, 
> something QNames are unable to do in a number of cases.
> 
> Let me put it differently: a QName is a valid CURIE. Moreover, a 
> QName, resolved according to CURIE rules, resolves to exactly the 
> same thing it would resolve to under QName rules. It's just that 
> there are some CURIEs that are not valid QNames.

(Apologies for leaping into a discussion which I probably haven't been
following
closely enough....)

Just to explore this a bit though...

The value space of the QName datatype is _not_ a set of URIs: it is (as Norm
pointed out)

> the set of tuples {namespace name, local part}, where namespace name 
> is an anyURI and local part is an NCName

http://www.w3.org/TR/xmlschema-2/#QName

i.e. (in the general case) an instance of the QName datatype does not
map to a
URI, though some XML formats (such as RDF/XML) do "layer" that mapping
on top of
the QName datatype - but even where that is the case - as I understand
it, at
least - that still doesn't change the fact that the value space of the QName
datatype is a set of {namespace name, local part} pairs, not a set of URIs.

What is the value space of the CURIE datatype? From the current version
of the
spec, I'm not quite sure, but given that the raison d'etre of CURIE is to
encode/represent URIs, I was assuming that the value space of the CURIE
datatype would be the set of URIs - not "the set of tuples {namespace name,
local part}"

If that is the case (and I recognise I may be drawing the wrong
conclusion and
it may not be!), then although the _lexical_ space of QName may be a
subset of
the lexical space of CURIE, the _value_ spaces of the two datatypes are
different. And if the value spaces are different, then I'm not sure it
is quite
correct to say "Moreover, a QName, resolved according to CURIE rules,
resolves
to exactly the same thing it would resolve to under QName rules."

Perhaps clarifying what the value space of the CURIE datatype is would help
clarify the distinctions between CURIE and QName?

* Goes back to lurking ;-) *

Cheers

Pete
-------
Pete Johnston
Research Officer (Interoperability)
UKOLN, University of Bath, Bath BA2 7AY, UK
tel: +44 (0)1225 383619 fax: +44 (0)1225 386838
mailto:p.johnston@ukoln.ac.uk
http://www.ukoln.ac.uk/ukoln/staff/p.johnston/
Received on Friday, 4 November 2005 16:00:38 GMT

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