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Re: SemWeb Non-Starter -- Distributed URI Discovery

From: Andy Powell <a.powell@ukoln.ac.uk>
Date: Sun, 10 Apr 2005 10:41:08 +0100 (GMT Daylight Time)
To: www-rdf-interest@w3.org
Message-ID: <Pine.WNT.4.56.0504101018000.-1910015@ulpc-ap-home.bath.ac.uk>

On Sun, 10 Apr 2005, Charles McCathieNevile wrote:

> >  I think it should be feasible to issue this sort of request:
> >  GET /food/blah HTTP/1.1
> > Host: example.com
> > Accept: application/rdf+xml
>
> Patrick replied
> >  Not to just jump in and jump out calously, but this has been
> > explored quite a bit for quite some time and content negotiation
> > is simply not the correct mechanism for this.
> >  C.f. the FAQ section of http://swdev.nokia.com/uriqa/URIQA.html ...
> >  Patrick
>
> I'm not so sure. I can see the problem if you see the world through URIQA
> glasses, but I think outside of that it is not a bad answer.

I tend to agree.  And I find the following answer in the URIQA FAQ
somewhat confusing...

--- cut ---

Why not use a MIME type and content negotiation to request a description?

Content negotiation is designed to allow agents to select from among a set
of alternate encodings. The distinction between a resource description and
(other kind of) resource representations is not based on any distinction
in encoding. In fact, a given description (which is itself a resource) may
have several available encodings (RDF/XML, XTM, N3, etc.).  Thus, if you
use content negotiation to indicate that you want a description, you can't
use it to indicate the preferred encoding of the description (if/when
other encodings than RDF/XML are available).

--- cut ---

...since (I think) it uses 'description' in the rather specialised sense
of 'concise bounded description'?  The first sentence would be better if
it read "Content negotiation is designed to allow agents to select from
among a set of alternate *representations*"?  In which case, given that a
description *is* a representation (and this is true even for a CBD), it's
hard to understand why content negotiation couldn't/shouldn't be used to
negotiate a 'description representation' or even a 'CBD representation'?

The problem (as outlined in the final sentence of the FAQ answer above) is
really with limitations in the current set of MIME types isn't it?
Couldn't much of what URIQA provides be achieved either by creating a new
type, 'cbd' (concise bounded description), wtih sub-types being used to
indicate particular 'encodings' - cbd/rdf+xml - or by concatenating cbd
into the sub-type - 'application/cbd+rdf+xml' ??

Sorry, I appreciate that this is probably going over old ground and that
I'm not familiar enough with the history of this discussion.  But the
answer in the FAQ doesn't seem, to me, to be a compelling reason to use
URIQA rather than content negotiation.

Andy
--
Distributed Systems, UKOLN, University of Bath, Bath, BA2 7AY, UK
http://www.ukoln.ac.uk/ukoln/staff/a.powell/      +44 1225 383933
Resource Discovery Network http://www.rdn.ac.uk/
Received on Sunday, 10 April 2005 09:41:10 GMT

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