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

Michael,

The original question you posed when starting the thread was this: If  
a1 and a2 are representations of resource a, then can we say anything  
about how “equivalent” they should be?

This question is unrelated to httpRange-14, only minimally related to  
RDFa, and only somewhat related to fragment ID semantics. Your  
question can be considered independently of all those other issues,  
and I think it would be a disservice to the TAG to broaden the  
question to include all those other areas at once.

Your axioms are concerned with the semantics of fragment IDs, that is,  
what does a URI of the form <xyz#foo> identify? I think this questions  
is adequately answered by RFC 3986, RFC 2616, and AWWW. It's well- 
trodden ground and I didn't see anyone articulate a reason for  
revisiting this part of the architecture. (You might well have such a  
reason (media fragments?), but don't make us speculate.)

Your axioms do not say anything new about

* httpRange-14 (which is concerned only with URIs of the form <xyz>,  
not <xyz#foo>),

* RDFa (which requires an update of the HTML/XHTML MIME type  
declarations, but no changes or clarifications of web architecture),

* the representation-equivalence question (which remains the same very  
thorny a question even if none of the representations define any  
fragment IDs).

Hence I really don't know what you are trying to achieve with your  
proposal :-(

Best,
Richard


On 19 Feb 2009, at 10:26, Michael Hausenblas 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.
>
> 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 15:54:01 UTC