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RE: [httpRedirections-57] Resource-Decription Header: a possible proposal to consider.

From: Booth, David (HP Software - Boston) <dbooth@hp.com>
Date: Fri, 8 Feb 2008 08:32:52 +0000
To: Jonathan Rees <jar@creativecommons.org>, "Williams, Stuart (HP Labs, Bristol)" <skw@hp.com>
CC: "www-tag@w3.org" <www-tag@w3.org>, Graham Klyne <GK@ninebynine.org>, Jonathan Borden <jonathan@openhealth.org>
Message-ID: <184112FE564ADF4F8F9C3FA01AE50009DED0FC6B55@G1W0486.americas.hpqcorp.net>

> From: Jonathan Rees
>
> On Feb 6, 2008, at 8:11 AM, Williams, Stuart (HP Labs, Bristol) wrote:
> > Resource-Description: http://example.org/site.rdf
> ...
> > This is stronger than the "303 'try-over-there <Location:>' 'hint'"
> > because the intention of the Resource-Description: is (or would be)
> > clear.
> ...
> > (Tracker, this is ISSUE-57)
>
> I think Link: as suggested by Richard is very similar, and has the
> advantage that it is already part of an HTTP spec. The suggestion has
> come up before. Unfortunately Link: disappeared in the move from 1.0
> to 1.1, if I remember my previous research on this correctly.
>
> The other advantage over 303, to me probably more important than the
> ability to adopt a rule saying that the target is supposed to be a
> description, is that it gives you a standard channel for
> communicating metadata for information resources (200) that don't or
> can't carry their own. This would be important for a wide variety of
> applications, including provenance, versioning, licensing, and site
> policy, that currently have to be layered in awkward ways on top of
> HTTP.

You don't have to bake anything in to HTTP to do that.  A 303 redirect can be used with an awww:InformationResource just as it can be used with anything else.  So for example, a URI such as

        http://example/doc/ir

can be used to denote an awww:InformationResource, and when it is dereferenced, it can 303-redirect to something like

        http://example/doc/metadata

and when that is dereferenced it can return a 200 OK with the RDF metadata that you want, such as (in n3):

        <http://example/doc/ir> hasProvenance prov:whatever .
        <http://example/doc/ir> hasVersion "1.20" .
        <http://example/doc/ir> hasMd5Checksum "567990020087678940" .
        <http://example/doc/ir> hasBitsAt "http://example/doc/bits" .
        <http://example/doc/ir> owl:sameAs <http://example/doc/bits> .

And dereferencing http://example/doc/bits can yield a 200 OK with whatever bits you were trying to denote.  Note that http://example/doc/ir would be the URI that you would want to publish -- not http://example/doc/ir , even though they denote the same awww:InformationResource.

Anyone (or any group) can write a specification that details exactly what conforming implementations should do to follow these conventions.  People may or may not follow them, just as they may or may not use a new HTTP header if it is added to the HTTP spec.  Defining a new HTTP header will not force people to adopt it, just as defining conventions like these will not force people to adopt them.

> [ . . . ]
>  The only other route I can think of
> (other than variant GETs, which have been ruled out) is a
> deterministic syntactic rule to go from a thing's URI to the URI of a
> description of the thing, in the situation where the first URI has no
> #. You would then "go" from the first URI to the second on the
> client, and do a GET of the second. I think it's probably too late in
> the game for this.

No it isn't.  Anyone can (nondestructively) layer their own syntactic conventions on top of http URIs, as I have previously described:
http://dbooth.org/2006/urn2http/

A good example of this is http://thing-described-by.org .  Suppose you come across the RDF triple

        _:foo _:fum <http://thing-described-by.org?http://dbooth.org/2005/dbooth/> .

and you want to find metadata about the resource denoted by
http://thing-described-by.org?http://dbooth.org/2005/dbooth/ .  If you dereference the URI, you will find that it 303-redirects to
http://dbooth.org/2005/dbooth/
which is a page containing such metadata.  (The page happens to be written in English, but it could just as well have been written in RDF.)  However, as described in
http://thing-described-by.org/#optimizing
if you know thing-described-by.org's conventions, which could certainly be written into a specification if desired, there is no need to dereference
http://thing-described-by.org?http://dbooth.org/2005/dbooth/
to determine that
http://dbooth.org/2005/dbooth/
contains the desired metadata.  Instead, the URI prefix
http://thing-described-by.org?
can be stripped off automatically to yield the desired metadata URI.

There may still be some benefit of convenience in adding a Resource-Description:  HTTP header, but all of the stated problems that such a header solves can be solved in other ways.


David Booth, Ph.D.
HP Software
+1 617 629 8881 office  |  dbooth@hp.com
http://www.hp.com/go/software

Opinions expressed herein are those of the author and do not represent the official views of HP unless explicitly stated otherwise.
Received on Friday, 8 February 2008 08:33:51 GMT

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