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RE: statements about resources vs. representations

From: Booth, David (HP Software - Boston) <dbooth@hp.com>
Date: Fri, 21 Nov 2008 17:48:44 +0000
To: Jonathan Rees <jar@creativecommons.org>
CC: "public-awwsw@w3.org" <public-awwsw@w3.org>
Message-ID: <CD2B872281385A439B98164F5351E6DD39C3A9ADB5@GVW1144EXB.americas.hpqcorp.net>

> From: Jonathan Rees
>
> (Using "representation" in the AWWW sense here.)
>
> Suppose I have a resource R, and for some reason I believe that
> R dc:creator author:Charles_Dickens.
>
> Now suppose that I do a GET to obtain a representation, and let F be
> the fixed resource (see [1]) whose representation is this
> representation.

So F is *some* fixed resource that happens to have this as its representation?

> (I'll need a term for the coercion of representation to fixed
> resource, so
> I'll say "the FR of the representation.")

So you're saying that for the representation, P, of R, a fixed resource F is created such that all representations of F are P, correct?

>
> Assuming good faith and proper functioning on everyone's part,
> can I conclude that F dc:creator author:Charles_Dickens . ?

That depends on the semantics of dc:creator.  On the surface, the assertion

   R dc:creator author:Charles_Dickens .

is merely an assertion about resource R, but indirectly it may be an assertion about the various representations of R, depending on the definition of dc:creator.  I suspect that most interpretations of the current definition of dc:creator *would* lead you to conclude that each representation of R was created by author:Charles_Dickens, but in theory dc:creator could be defined differently.

For example, suppose I have a web site that emits the text of Moby Dick one word at a time, one word per representation.  One would *not* claim that author:Charles_Dickens created the individual words, but one might nonetheless assert some kind of creation relationship between author:Charles_Dickens and resource R, because R is an *encoding* of the Moby Dick text.

> I suspect
> so, but is this idea codified anywhere? Wouldn't this be part
> of AWWSW?
>
> It seems to me that some properties will be shared between a resource
> and its representations' FRs, while others aren't.
>
> E.g. a property containsWord could easily be true of one
> representation
> but not another (e.g. if the representations differ by language). Or,
> more obviously,
> one can meaningfully talk about the media type and
> content-length of a FR,
> but not necessarily of its originating resource.

That would be a shorthand though, relying on the fact that a FixedResource always produces the same represention, because media type and content length really apply to representations -- not resources.

> Volatility
> is similar: the FR
> is by definition not time-varying, but the resource may be.
>
> I guess this is what Tim's "generic resources" memo [1] is saying.
>
> Are there any properties of a resource that can be inferred
> from its representations?

Well, if you believe that an InformationResource (which is the only thing that *can* have an awww:Representation) is essentially a function from (Request x Time) to awww:Representations, then the answer is very simple: knowing the representation tells you almost nothing about the resource.

> That is, when I do a GET, do I
> (or rather a stupid automated agent) learn anything
> at all about what the resource is?

Yes.  You learn that it is an awww:InformationResource.  If you choose to read and believe the content of the returned representation then you might learn a lot more, but the successful GET response itself tells you only that it is an awww:InformationResource.

See lines 150-159 of http://esw.w3.org/topic/AwwswDboothsRules :

150. # httpRange-14 rule: 200 response => InformationResource
151. # http://lists.w3.org/Archives/Public/www-tag/2005Jun/0039.html
152. {       ?r uri:hasURI ?u .
153.    ?u http:hasGetReply ?reply .
154.    ?reply http:hasStatusCode 200 .
155.    # ("FIRED: " ?r " a awww:InformationResource \n") string:concatenation ?fired .  # Debug
156. } => {
157.    ?r a awww:InformationResource .
158.    # "a" log:outputString ?fired .  # Debug
159.    } .

> I certainly don't learn anything
> about, say, volatility, unless we're lucky enough to have
> a credible assertion about it in the representation.
> But I would guess that at least for things like authorship
> (aspects of the content), if P and Q are disjoint classes,
> and P applies to a resource's representation's FR, then you
> can conclude that
> Q does not apply to the resource? That is, if you find that
> any representation's FR's creator list consists of {George
> Eliot}, then
> you know that the resource's creator list cannot be {Charles Dickens}.
>
> This doesn't hold for volatility: volatile and nonvolatile
> are disjoint.
>
> Conjecture: It seems that this analysis could continue, e.g.
> by helping
> one to understand the domain, range, and arity (functional, inverse
> functional, etc.) of various properties such as authorship
> and volatility
> that one might apply to (information) resources.
>
> [1] http://www.w3.org/DesignIssues/Generic.html
>
> P.S. Is anyone interested in the AWWSW group any more?

At the last Cambridge get-together of the Semantic Web IG (which was *very* well attended, BTW -- I think TimBL took a head count, though I didn't), someone specifically asked me why the AWWSW list had been so quiet lately, and commented that the work is really important.  And *I* am certainly still very interested, though unfortunately my other work responsibilities have made it very difficult to get anything done on it lately.


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

Statements made herein represent the views of the author and do not necessarily represent the official views of HP unless explicitly so stated.
Received on Friday, 21 November 2008 17:50:23 GMT

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