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

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Thu, 17 Jul 2003 17:33:41 +0300
Message-ID: <002801c34c70$715686d0$330da20a@NOE.Nokia.com>
To: "Walden Mathews" <waldenm@optonline.net>, "ext Tim Bray" <tbray@textuality.com>, "Jonathan Borden" <jonathan@openhealth.org>
Cc: "pat hayes" <phayes@ihmc.us>, <www-tag@w3.org>, "Pat Hayes" <phayes@ai.uwf.edu>


----- Original Message -----
From: "ext Walden Mathews" <waldenm@optonline.net>
To: "Patrick Stickler" <patrick.stickler@nokia.com>; "ext Tim Bray"
<tbray@textuality.com>; "Jonathan Borden" <jonathan@openhealth.org>
Cc: "pat hayes" <phayes@ihmc.us>; <www-tag@w3.org>; "Pat Hayes"
<phayes@ai.uwf.edu>
Sent: 17 July, 2003 16:51
Subject: Re: "On the Web" vs "On the Semantic Web" (was Re: resources and
URIs)


> Patrick,
>
> One nit.  In at least two places you assert that the web is a network
> of [physically] linked representations.  But for all I can tell, while the
> links originate in representations, they don't terminate in them.  So
those
> statements are a little misleading.  I think it's more accurate to say
that
> the links terminate in functions, which have representations in their
range.

Quite so. I was thinking along the lines that a representation
is linked to all representations accessible via references to
representations by their URIs.

I.e. the physical part of the Web allows traversal between
representations, not resources, and one moves from representation
to representation.

It is, though, quite true that there is an element of indirection
in the links themselves, dependent on the set of representations
each server exposes for the resources in question.

I think I would be OK will the function based view you suggest,
such that it is the function that "instantiates" or "defines"
the unidirectional links from one representation to others.

But I think you can still view the physical dimension of
the web as a network of interlinked representations (despite
the fact that the end points of the links are not explicit
in any given source representation).

> I don't know if that affects your arguments below,

I don't think so.

> which otherwise
> seem quite reasonable to me.

Cool. Though I expect that certain folks will tear it
apart one way or another (not that there's anything wrong
with it, mind you ;-)

Cheers,

Patrick


> Walden
>
> ----- Original Message -----
> From: "Patrick Stickler" <patrick.stickler@nokia.com>
> To: "ext Tim Bray" <tbray@textuality.com>; "Jonathan Borden"
> <jonathan@openhealth.org>
> Cc: "pat hayes" <phayes@ihmc.us>; <www-tag@w3.org>; "Pat Hayes"
> <phayes@ai.uwf.edu>
> Sent: Thursday, July 17, 2003 5:43 AM
> Subject: "On the Web" vs "On the Semantic Web" (was Re: resources and
URIs)
>
>
> >
> >
> > Jonathan Borden wrote:
> >
> > > > > If we are going to concern the "SW" at least as it is incarnated
in
> > current
> > > > activities and specific software products (i.e. RDF and OWL related
> > > > software), then you may certainly be a part of the Web without a
URI.
> > Hence
> > > > the statement is not correct in the SW context -- I'm not entirely
> > convinced
> > > > that it is correct in the 'current Web' context e.g.
> >
> > To which Tim Bray responded:
> >
> > > This might be a nice clear clean differentiating principle, because
I'm
> > > pretty convinced that at the moment, something that doesn't have a URI
> > > isn't part of the Web.
> >
> > I think Tim's distinction is valid. A resource not denoted by a URI is
> > not "on the web".
> >
> > The Web and the Semantic Web are (IMO) two distinct things which
> > intersect via a common set of URIs with (presumed) consistent
> > denotations.
> >
> > Here's how I've been viewing the relationship between the Web
> > and Semantic Web:
> >
> > The Web is a network of linked representations of resources, where
> > those representations are accessible via URIs. Thus it is quite correct,
> > I think, to say that a resource that is not denoted by a URI is not "on
> > the web". In fact, I think an even tighter claim can be made -- that a
> > resource that is not denoted by a URI that is meaningful to the HTTP
> > protocol and does not intentionally** resolve to at least one
> representation
> > is not "on the web".
> >
> > ** barring practical technical problems such as system being offline,
> >      routing updates/problems, etc. etc. i.e. the authority for the URI
> >      intends that the URI will reliably resolve to a representation.
> >
> > Thus, a URI that consistently and expectedly always produces a 404 error
> > does not denote a resource that is "on the web", even if the URI is used
> > in some non-web fashion to actually denote some resource.
> >
> > And here's an important point, that addresses concerns expressed by
> > Pat and Jonathan:  a resource that is "on the web" is not (necessarily)
> > itself part of that physically realized network of interlinked
> > representations
> > managed by web servers. Nor is every representation necessarily
> > "on the web" (if it is not unambiguously denoted by its own URI).
> >
> > Being "on the web" simply means that the resource in question is
> > denoted by a URI which can be resolved via HTTP to a representation.
> > And that representation may contain references to other resources
> > which may resolve to other representations, etc.
> >
> > The only resources which are both "on the web" and part of that physical
> > network of representations are representations which are denoted by URIs
> > which resolve to a bit-equal copy of themselves.
> >
> > One can say that there are two realizations or facets or dimensions
> > of the Web:
> >
> >    (1) the physical network of interlinked representations managed by
> >          HTTP servers
> >
> >    (2) the abstract network of interrelated resources having interlinked
> >         representations managed by HTTP servers.
> >
> > Thus, any resource whatsoever may be "on the web", such as a star
> > cluster, by being denoted by a URI which is meaningful to HTTP and
> > resolves to one or more representations. That doesn't mean that that
> > star cluster is part of the physically linked network of
representations.
> > But it is still "on the web" and thus one may interact with
> representations
> > of that resource via the web machinery.
> >
> > This distinction between being "on the web" and being part of the
> > physical network of representations is one that I think needs to be
> > clarified in the TAG's web architecture document.
> >
> > The Semantic Web also has two realizations or facets or dimensions:
> >
> >     (1)  a virtual (ever changing) global graph of statements (both
> explicit
> >           and inferrable) constituting the sum of knowledge available to
> > agents
> >           at any given time, even though any given agent or physical
> > knowledge
> >           base may (usually always will) possess only a fraction of that
> > virtual
> >           all inclusive graph
> >
> >     (2) an implicit network of interrelated resources related by
> statements
> > in
> >           that graph.
> >
> > --
> >
> > "On the Web" vs "On the Semantic Web":
> >
> > A given resource may be "on the web" yet not "on the semantic web"
> > because even though that resource is denoted by a URI which resolves
> > via HTTP to a representation, there may exist no statement referring to
> that
> > resource. The moment such a statement is asserted, that resource is
> > then "on the semantic web". Since a given SW agent or KB will nearly
> always
> > possess only a subgraph of that virtual global graph that is the SW, it
> > will in practice never be possible to conclude absolutely that a given
> > resource is not on the semantic web.
> >
> > A given resource may be "on the semantic web" yet not "on the web"
because
> > even though that resource is referred to in one or more statements it is
> > is not denoted by a URI that is meaningful to HTTP and intentionally
> > resolves to one or more representations. The moment that resource is
> > denoted by a URI that resolves via HTTP to a representation, it is then
> > "on the web". Since a given web application may not be aware of all URIs
> > synonymously denoting the resource in question, it is unlikely that a
web
> > application can ever conclude absolutely that a given resource is not on
> the
> > web.
> >
> > Thus, the intersection of the Web and Semantic Web constitutes those
> > resources which are both (a) denoted by URIs that are meaningful to HTTP
> > and intentionally resolve to at least one representation and (b) are
> > referred
> > to in at least one statement in that virtual, global graph that is the
SW.
> >
> > Yet for both the Web and the Semantic Web:
> >
> > 1. We are talking about the same infinite set of resources, namely
things
> >      in the universe, with the Web and Semantic Web embodying finite
> >      subsets of that infinite set of resources.
> >
> > 2. URIs serve the same function for both the Web and the Semantic Web,
> >     namely they denote resources. The Web provides machinery for
> >     interacting with representations of the denoted resources. The
> Semantic
> >     Web provides machinery for interacting with formal descriptions of
> >     the denoted resources. But the denotation (is presumed to) remain
> >     consistent for a given URI irrespective of Web or Semantic Web
> >     operations.
> >
> > --
> >
> > This brings us to a single critical missing piece to this puzzle,
namely,
> > how SW agents consistently and reliably access authoritative
> > descriptions about resources in a standardized way which is
> > analogous to how web clients access authoritative representations
> > of resources.
> >
> > This is where I see solutions like URIQA [1] playing a crucial role, by
> > providing that missing key piece of Semantic Web architecture.
> >
> > Regards,
> >
> > Patrick
> >
> > --
> >
> > Patrick Stickler
> > Nokia, Finland
> > patrick.stickler@nokia.com
> >
> > [1] http://sw.nokia.com/URIQA.html
> >
> >
>
>
>
Received on Thursday, 17 July 2003 10:33:58 UTC

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