W3C home > Mailing lists > Public > www-rdf-interest@w3.org > November 2003

Re: MGET and machine processing

From: Mark Baker <distobj@acm.org>
Date: Tue, 25 Nov 2003 21:02:34 -0500
To: Patrick Stickler <patrick.stickler@nokia.com>
Cc: www-rdf-interest@w3.org
Message-ID: <20031125210234.J1020@www.markbaker.ca>

On Tue, Nov 25, 2003 at 07:21:49PM +0200, Patrick Stickler wrote:
> On Monday, Nov 24, 2003, at 16:55 Europe/Helsinki, ext Mark Baker wrote:
> 
> > On Mon, Nov 24, 2003 at 02:41:34PM +0200, Patrick Stickler wrote:
> >> Well, while I consider it acceptable to treat a description as
> >> a representation, it is nonetheless necessary to be clear about
> >> the distinction when interacting with the server.
> >
> > Right.  Using a different URI would be another way to do that! 8-)
> 
> Both representations *and* descriptions are distinct resources
> from the resource denoted by a request URL (except for the special
> case where the resource is a digital entity and the representation
> is a bit-equal copy of it).

Absolutely.

> So whether you are asking the server for a representation or
> a description, you should (usually) expect to get back *something
> else* and have the URI denoting that something else specified
> in the response header.
>
> But one cannot know, from some URI, what some *other* URI denoting
> a description of the thing denoted by the first URI might be, no
> more so than one can know what URI might denote a representation
> returned for some request having a *different* request URI.

Yup.  You use a new method on a URI to return a description, which
is given a URI upon which subsequent GETs can return it.  I use a
GET or HEAD on the original URI to return a new header which
communicates the URI of the description resource, upon which I can
invoke GET.

The trade off is an extra round trip and a new header, for a new method.
IMO, that's akin to trading a pawn and a bishop (respectively) for a
queen.

> No. Content negotiation does *not* do the job. And we will want
> to use content negotation *as* content negotiation, for requesting
> different possible encodings of descriptions.
> 
> I've pointed this out before.
> 
> In short, content negoation does not work, nor should it be overloaded
> in this fashion, as the semantic distinction between description and
> (other form of) representation has nothing whatsoever to do with
> encoding (even if RDF/XML is a default encoding for descriptions).

What you've pointed out before - and presumably what you're referring to
there - was that it is incorrect to use content negotiation to negotiate
for descriptions from the URI which is being described, and I agree
completely.  But I can safely negotiate for RDF/XML *representations*
using the URI.

Mark.
-- 
Mark Baker.   Ottawa, Ontario, CANADA.        http://www.markbaker.ca
Received on Tuesday, 25 November 2003 21:01:06 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 December 2009 10:52:03 GMT