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

From: Jonathan Rees <jar@creativecommons.org>
Date: Thu, 19 Feb 2009 10:07:47 -0500
Message-ID: <760bcb2a0902190707x4723b6cald483405b86bee13b@mail.gmail.com>
To: Michael Hausenblas <michael.hausenblas@deri.org>
Cc: "www-tag@w3.org" <www-tag@w3.org>, timbl@w3.org, Richard Cyganiak <richard@cyganiak.de>
Questions for clarification only, to make sure I understand what you are saying.

On Thu, Feb 19, 2009 at 5:26 AM, Michael Hausenblas
<michael.hausenblas@deri.org> wrote:
>
> 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.

Do I understand you as making a definition thing = non-information
resource? Or did you mean to say "not *necessarily* conveyed"?

Are you talking about all URIs or just http: and https: URIs?

> 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].

By "the resource" do you mean the resource named by (a) the fragmentless URI, or
the resource named by (b) the fragmentful URI?

> 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].

Same question as above re "the resource". Also, if specs or media
types say inconsistent things about the referent of the the
fragmentful URI, what then? E.g. suppose one media type implies that
the fragementful URI identifies, say, an ontology, while another says
it identifies a table? Wouldn't it be reasonable to believe that no
information resource can simultaneously be an ontology and a table -
even if the URI owner asserts that the representations are
"sufficiently consistent"? Hypothetically speaking of course.
>
> 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].

You do not mean to be exclusive here right? The owner could also
communicate by any other communications protocol such as FTP or URIQA?
Do you mean an application might want to treat communications from the
URI owner differently based on the choice of protocol, or make
assumptions based on the absence of a communication along a particular
kind of channel?

> ===
>
> Please note the following: The intention is to keep the current definition
> of IR as of the AWWW1

You are aware that there is some debate around the desirability of doing so?

> 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.

Could one phrase this as a defaulting mechanism: In the absence of evidence
to the contrary, one should assume that a fragmentless URI "identifies" an
information resource?  You are aware that this runs afoul of the
established practice of communicating non-IR-ness in "description resources"
obtained in other ways - do you mean to ask people to change what they do?

> 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.

So communications from the URI owner along certain paths are operationally
to be treated in one way, while communications along other paths are
to be treated
in another?

Can you say more about what practical (non-philosophical) problem
you're up against here?

Best
Jonathan

>
> @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

good set of references, thanks.

> --
> 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 15:08:29 GMT

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