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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: Michael Hausenblas <michael.hausenblas@deri.org>
Date: Thu, 19 Feb 2009 18:17:07 +0000
To: Jonathan Rees <jar@creativecommons.org>
CC: "www-tag@w3.org" <www-tag@w3.org>
Message-ID: <C5C352A3.2162%michael.hausenblas@deri.org>

Jonathan,

> Do I understand you as making a definition thing = non-information resource?

Basically, yes.

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

As a good Web citizen, of course HTTP URIs in the first place (unsure about
https scheme - can you provide me with pointers re discussions around this,
please?)

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

My idea was (put in simple word): let's use fragmentful URIs from now on to
identify non-information resources, ahm, things. As there are already used
conventions/specs (for example HTML fragments, RDF fragments, etc.) one
needs rules to explicitly state exceptions to that default.

> 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?

Honestly, I don't understand the question. Can you rephrase, please?

>> 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?

Not exclusive, but I get more and more the feeling that people need concrete
advices (or is it just me?) on certain issues.

>> 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?

Yes.

> 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?

So far I have not explicitly talked about fragmentless URIs, my bad. Yes, my
assumption would be that fragmentless URI per default would then identify
IRs unless one explicitly says this is not the case (again, similar as of
axiom 3 and 4). When you are talking about 'established practice': how big
would the 'collateral damage' be, in your opinion?


>> 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?

Not sure if I understand you right, here. All I am saying is that *I*
identify/propose two mechanisms to deploy POWDER's describedby property.
There might be more to add to this list; these can be seen as good practices
- is this against any doctrine, here?

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

Problem: what is the definition of a non-information resource? AWWW1 doesn't
talk about it, and I was not able to spot a definition in other docs - have
you? Looking at [1], I guess it is a rather hard task, currently ;)

Cheers,
      Michael

[1] http://esw.w3.org/topic/AwwswVocabulary

-- 
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/


> From: Jonathan Rees <jar@creativecommons.org>
> Date: Thu, 19 Feb 2009 10:07:47 -0500
> To: Michael Hausenblas <michael.hausenblas@deri.org>
> Cc: "www-tag@w3.org" <www-tag@w3.org>, <timbl@w3.org>, Richard Cyganiak
> <richard@cyganiak.de>
> Subject: Re: Last minute input to discussion re 'on the boundaries of content
> negotiation in the context of the Web of Data'
> 
> 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 18:17:55 GMT

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