Re: [pedantic-web] Re: The OWL Ontology URI

On Thu, 2010-05-13 at 00:03 -0500, Pat Hayes wrote:
> Dan, I don't think I've got my point across, and its getting lost in  
> all this confusion about information resourceness. Its really a very  
> simple point, and I can make it with a very simple example.  Suppose A  
> is an RDF graph, and B is an RDF/XML file which encodes/is a surface  
> syntax of/represents (choose your favorite terminology) that graph A.  
> And suppose U is a URI which "identifies" B, in the sense that what  
> you get back, when you do an HTTP GET using U, is a  
> 'representation' (in the REST sense) of B with a 200 code attached.  

As I say, I misread that bit there. Oops.

> That is, the relationship between U and B is exactly like that between  
> the URI of a web page, and the web page itself.
> 
> My point is simply that under these circumstances, we are pretty much  
> obliged by http-range-14, as I understand it, to say that U denotes B;  
> that is, it denotes the thing it HTTP-identifies.

I think that httpRange-14 has little/nothing to add here;
we're obliged to say that U denotes B as soon as we suppose
that U is a URI which identifies B. Perhaps that's just my
way of looking at things... but I'm pretty sure that httpRange-14
is unrelated.

In any case, I stipulate to this much.


>  And if it denotes B,  
> then it cannot denote A, since (for other reasons, on which we agree)  
> A is not identical to B.

Agreed.

>  As for being an information resource, as I  
> say I see this as secondary and not particularly important, but I  
> would observe that surely if anything can be an information resource,  
> then B *certainly* is one; and that this is all that is necessary for  
> the argument to go through.

No, if you're trying to establish that a graph cannot be
an information resource, you're not there yet; you've over-constrained
the premise by saying that U identifies B, an RDF/XML document.

>  Even if A is an information resource, U  
> cannot refer to it, since B's claim upon the reference of U is prior  
> to, and based on a more secure case than, A's.
> 
> If you want to object that there is no natural priority here,

I think I do... that is: I feel obliged to, on behalf of some
of the community...

>  and that  
> we humans can simply assert by fiat that the referent of U is whatever  
> we decide it should be, in particular it could be A, I would make the  
> following replies. First, the parallel with 'normal' URI usage in the  
> non-semantic Web seems to me to be compelling.

That was certainly TimBL's position. Roy countered that U may
well identify a coffee machine or a robot, whose state you can GET.
I think he exhibited actual examples of such. Tim countered
that U didn't refer to the coffee machine per se, but a
web page about the coffee machine. And round we go.

>  (In fact, surely this  
> was the primary motivation for the http-range-14 decision in t he  
> first place? That is, we all have to admit that the pre-semantic Web  
> uses URIs to effectively 'name' things like Web pages, and it would be  
> folly to adopt a SWeb convention that tried to deny this.)

Yes, that is the motivation.

>  Second, if  
> we decide in this example that U denotes A, how can anyone ever refer  
> to B?

(a) who says they should/must be able to? We don't demand that every
IP packet naturally gets a URI name; why HTTP reply contents?

(b) of course they can*: just mint another URI for it.

*modulo copyright issues etc.

>  With this convention, B has become semantically invisible, an  
> unnameable entity. But B is surely as "real" as A is, in fact if  
> anything it has more of a claim to be a real computational entity, as  
> opposed to (what some would call) a mere abstraction. B may for  
> example have a provenance, an author, a date of creation and even a  
> financial value, none of which could possibly apply to a purely  
> Platonic entity such as A. (Remember, an RDF graph is a *set*.)

You sound remarkably like TimBL ;-)

This is the sort of argument he gives for why integers
are not information resources. He offers this sort of
axiom to the community, but some (e.g. Sandro) don't buy it.

Perhaps we could offer it to them again, in a nicer package?
i.e. with better motivation?

>  And  
> third, the relationship between A and B is highly asymmetric. Given B,  
> one can compute A. B has all the information about A. But not the  
> reverse: A is simply a set, and has no information about how this set  
> is syntactically encoded in a linear convention that can be put into a  
> byte stream.

I don't really see what that has to do with the price of tea in China;
that seems an unremarkable aspect of the relationship between
some resources and their representations.

Well... maybe it would appeal to some people. But it doesn't to me
just now.

> I think (?) you understood me to be saying that U denotes the  
> 'representation' of B, rather than B itself. However, that was not my  
> intention. Part of the problem we have here is that this word,  
> "representation" has acquired a technical meaning in this area of  
> discussion which is rather different from its general meaning (or  
> maybe more accurately, a very, very narrow subcase of the more general  
> meaning.)

I'd be happy to use http-200-response-content, for the purposes
of some period of discussion. (though that suggests the resource
is doing the responding, which, as Jonathan points out,
might be more than we want to say).

>  As used in Roy's thesis and the subsequent literature, where  
> it is the R in REST, it has the very special meaning of the  
> relationship between an HTTP message body and the file or perhaps  
> script that emits this body at the HTTP endpoint. I do not pretend to  
> be able to give, or even fully understand, the full nuances of  
> architectural finesse that are involved in stating this properly, but  
> it certainly requires both the 'representation' and the thing  
> 'represented' to be things in a computer memory,

Well... what if the computer has a thermometer attached...
or a camera or microphone... or is connected to the stock
market by a network... or it has a regularly-updated
index of the whole web. It gets blurry kinda quickly.

>  which have an  
> especially close relationship to one another in that the former can  
> completely 'capture' the latter, without loss of information. My own  
> intuitive picture of this is simply that of a file copy, or the taking  
> of an imprint from a platen in a hand press. But the relationship  
> between (for example) a photograph of me and me; or between an RDF  
> description of the familial relationships among a group of people, and  
> the actual people; or between the XML file B and the abstract graph A,  
> are not this kind of 'representation' at all.

Again, you sound remarkably like TimBL. The waffly definition
of "information resource" is the result of a clash between him
and other TAG members and community members who found that
position overly constraining.

>  So it is easy to get  
> muddled when we use this word carelessly (as I admit to doing in the  
> previous message.)
> 
> Pat

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
gpg D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E

Received on Thursday, 13 May 2010 22:30:16 UTC