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Re: "On the Web" vs "On the Semantic Web" (was Re: resources and URIs)

From: pat hayes <phayes@ihmc.us>
Date: Mon, 21 Jul 2003 19:24:58 -0500
Message-Id: <p06001a0cbb42314eda87@[10.0.100.23]>
To: "Jonathan Borden" <jonathan@openhealth.org>
Cc: "Michael Mealling" <michael@neonym.net>, <www-tag@w3.org>

>----- Original Message -----
>From: "pat hayes" <phayes@ihmc.us>
>To: "Tim Bray" <tbray@textuality.com>
>Cc: "Michael Mealling" <michael@neonym.net>; <www-tag@w3.org>
>Sent: Monday, July 21, 2003 1:04 PM
>Subject: Re: "On the Web" vs "On the Semantic Web" (was Re: resources and
>URIs)
>
>
>>
>>  >pat hayes wrote:
>>  >
>>  >>PS.  Reading things like this makes me wonder whether you guys
>>  >>inhabit the same planet as the rest of us. Things with hearts and
>>  >>multiple interfaces, arranged in layers...?? What the hell are you
>>  >>talking about??? Here I am looking out of my window at an oak tree
>>  >>and I wonder if its a resource, and what its interfaces could be,
>>  >>and what layer it would be in....
>>  >
>>  >If someone publishes an URI for it
>>
>>  How could anyone tell whether a URI was 'for' an oak tree? You said
>>  it yourself:
>>
>>  [PH] Am I identified by a URI? How could anyone possibly tell?
>>
>>  [TB] You're right; the current web architecture provides no way to
>>  test this condition.
>>
>>  >and, even better, provides representations (and even, better the
>>  >representations include audio and video and photos), then yes, that
>>  >oak tree is on the Web as far as I, or any software I write, can
>>  >tell.
>>
>>  I doubt if you or anyone else could write software that could tell
>>  whether an oak tree was or was not connected with the Web in any way
>>  at all. At the very least, you would need to have a very advanced
>>  piece of visual recognition software; to get a particular tree you
>>  would need to have it incorporated into something that knew where it
>>  was and where it was looking at. You need something like a webcam
>>  linked to a GPS and a compass running an AI vision system that knew a
>>  lot about botany.
>>
>>  But look, aside from this, your answer makes being 'on the Web'
>>  meaningless. Its not an architectural condition, obviously. It does
>>  not correspond to 'having a URI' since the URI could identify an
>>  image of the tree just as well as the tree itself; and in fact if the
>>  URI starts 'http:' and ends with a fragID then it is required to
>>  indicate an anchored place in an HTML document, not the thing
>>  'denoted' - if there is a single such thing, which is extremely
>>  doubtful - by the picture or text found at that anchored location.
>>  What if the anchored location is a piece of text which describes an
>>  entire situation involving lots of entities? Which of them is THE
>>  resource that the URI is supposed to indicate? What if it is a
>>  picture of three trees? A drawing of Yggdrasil?
>
>You are caught in the resource/representation bug.

Actually Im dancing between the alternatives trying to make sense of 
the TAG document.  (You know, Jonathan, the use/mention distinction 
is one that I am reasonably well acquainted with:-)

>What you get when
>resolving a HTTP URI with a fragid _might be_ an HTML document. It is the
>responsability of the client to use the fragid to look inside the HTML
>_representation_

that is, the document, which itself is a representation, right?

>  to find an anchored piece of the HTML document. This is all
>the _representation_ not the resource.

OK, Im fine with that so far.

>ndeed the same HTTP URI with fragid,
>might be resolved with Accept: appliction/rdf+xml in which case your same
>fragid identifies an RDF description (i.e. rdf:ID="frag"), now what? You
>still don't have the actual resource, rather an RDF/XML representation.

If the resource is what is denoted, you almost never actually get the 
resource.  On the other hand, if the resource is what you get the 
thing that you get from, then its almost never what is denoted. Which 
is it?? I still havnt got a clear answer. The TAG architecture 
document, and RFC 2396, both read like they were written by 
committees half of which thought one way and half thought the other 
way.  Oddly enough.

>
>If we _were to_ properly integrate the SW with the current Web, we _might
>say_ that when an RDF/XML representation is returned, it ?is a full fidelity
>representation of the actual resource?

No, the only rational thing to say is that it is a representation. If 
ever something could be properly called a representation, an RDF/XML 
document would be one of those.

>Nope that doesn't work, so how ought
>this work? What ought the connection be between a piece of so-located
>RDF/XML and the resource it describes?

Er.... that it describes it? That it - the resource - is (part of, in 
some sense made exact by the MT) a satisfying interpretation of the 
representation? THIS part of the overall picture is one that we do 
have pretty much worked out.

Of course, this doesn't fit with the doctrine that resources must be 
uniquely indicated by URIs, but that is provably nonsense in any case 
if resources are denoted by URIs, so can be safely ignored.

>The current SW specs i.e. RDF, don't
>address this issue _except_ that OWL does define what happens when an
><owl:import>s URI is dereferenced (which is why owl:imports is somewhat
>controversial). This seems to be a huge hole in the SW that needs fillin' --
>not the current Web's problem though.

We must not be communicating. The relationship between web ontology 
languages and whatever they refer to is one of the few topics we HAVE 
got worked out properly.

Pat
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Received on Monday, 21 July 2003 20:25:01 UTC

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