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Last minute input to discussion re 'on the boundaries of content negotiation in the context of the Web of Data'

From: Michael Hausenblas <michael.hausenblas@deri.org>
Date: Thu, 19 Feb 2009 10:26:58 +0000
To: "www-tag@w3.org" <www-tag@w3.org>, <timbl@w3.org>, Richard Cyganiak <richard@cyganiak.de>
Message-ID: <C5C2E472.2127%michael.hausenblas@deri.org>

Dear TAG members, Tim, Richard,

Short version: an attempt to defined non-information resources without using
non-information resource ;)

Long version:

In order to contribute in a constructive way to the discussion around
information resources, non-information resources, CN and 200/303 issues, I'd
like to propose the following, which may be taken as an input to my
previously raised issue around the boundaries of CN in the Web of Data use
case. To additionally address emerging usage of RDFa, this area has been
taken into account as well.

Please note that this is *not* a philosophical approach and I try to ground
all my terms and only use *existing* protocols, definitions, etc.:

===
Axiom 1) A URI containing a fragment identifier as of RFC3986 [1] identifies
a 'thing', that is, a resource which essential characteristics are not
conveyed in a message as opposed to an information resource as of AWWW1 [2],
unless otherwise stated.

Axiom 2) Iff the media type of a representation obtained by dereferencing a
URI (that is, performing an HTTP GET on the URI) defines the semantics of
the fragment identifier, the resource is an information resource as of [2];
this is the case 3 in [3].

Axiom 3) Iff the authoritative party as defined in section '2.2.2.1. URI
ownership' of [4], that is the one who can claim URI ownership, explicitly
states that fragment identifier semantics throughout different
representations are sufficiently consistent, the resource is an information
resource as of [2]; this is the case 1 in [3].

Axiom 4) An authoritative party can explicitly state fragment identifier
semantics consistency by using POWDER's describedby property as of [5] along
with HTTP Link: header as of [6] or by embedding RDF as of [7].
===

Please note the following: The intention is to keep the current definition
of IR as of the AWWW1 and clearly define what else is possible, hence to
make related (sometimes questioned and IMHO underspecified definitions such
as for example found in httpRange-14) more usable in a practical context.
The axiom 1 actually asks people to use frag-ID-URIs as the (one and only)
default to identify 'things', however, axiom 2 - 4 allow to create
exceptions based on an explicit set of actions. Further, axiom  allows
(currently) two ways to 'announce' exceptions, on the HTTP layer or on the
representation layer - this is open to discussion and should/will be
extended.

@Tim: Do you think this helps in getting closer to a written explanation of
your often articulated thoughts re 'sameness' of information obtained from
resources, as e.g. in [8]? And also: does this solve our issue wit RDFa as
discussed in [9]?

@Richard: Are the axioms consistent with the outcome of your analysis in
[10]?

Cheers,
      Michael

[1] http://tools.ietf.org/html/rfc3986#section-3.5
[2] http://www.w3.org/TR/webarch/#def-information-resource
[3] http://www.w3.org/TR/webarch/#frag-coneg
[4] http://www.w3.org/TR/webarch/#URI-collision
[5] http://www.w3.org/2007/05/powder-s#describedby
[6] http://tools.ietf.org/html/draft-nottingham-http-link-header-03
[7] http://www.w3.org/2001/tag/doc/selfDescribingDocuments#UsingRDFa
[8] http://chatlogs.planetrdf.com/swig/2009-02-09#T15-09-20
[9] http://esw.w3.org/topic/RDFa_vs_RDFXML
[10] http://lists.w3.org/Archives/Public/semantic-web/2007Dec/0157.html

-- 
Dr. Michael Hausenblas
DERI - Digital Enterprise Research Institute
National University of Ireland, Lower Dangan,
Galway, Ireland, Europe
Tel. +353 91 495730
http://sw-app.org/about.html
http://webofdata.wordpress.com/
Received on Thursday, 19 February 2009 10:27:44 GMT

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