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

From: Walden Mathews <waldenm@optonline.net>
Date: Thu, 17 Jul 2003 09:51:21 -0400
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>
Message-id: <002d01c34c6a$82d94fb0$0902a8c0@Walden>

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.

I don't know if that affects your arguments below, which otherwise
seem quite reasonable to me.

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 09:51:29 UTC

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