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Re: Denotation of URIs

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Tue, 08 Apr 2003 13:53:30 -0400 (EDT)
Message-Id: <20030408.135330.113729295.pfps@research.bell-labs.com>
To: Patrick.Stickler@nokia.com
Cc: zednenem@psualum.com, www-rdf-interest@w3.org

From: <Patrick.Stickler@nokia.com>
Subject: RE: Denotation of URIs
Date: Fri, 4 Apr 2003 15:29:36 +0300

> > -----Original Message-----
> > From: ext Peter F. Patel-Schneider 
> > [mailto:pfps@research.bell-labs.com]
> > Sent: 04 April, 2003 15:00
> > To: zednenem@psualum.com
> > Cc: www-rdf-interest@w3.org
> > Subject: Re: Denotation of URIs
> > 
> > 
> > 
> > From: David Menendez <zednenem@psualum.com>
> > Subject: Denotation of URIs (was: URI for language identifiers)
> > Date: Fri, 4 Apr 2003 02:13:02 -0500
> > 
> > > 
> > > At 7:49 PM -0500 2003-04-02, Peter F. Patel-Schneider wrote:
> > > >However, even
> > > >in this very expansive notion of property there are 
> > (still) considerable
> > > >``fair use'' provisions.  Hopefully these provisions will not be so
> > > >weakened that I will be prohibited from making the claim that the
> > > >denotation of http://www.whitehouse.gov/#43 is Tipper 
> > Gore's husband.
> > > 
> > > The only reason anyone might object to that would be if there was 
> > > already a widespread understanding that 
> > > <http://www.whitehouse.gov/#43> denotes "The 43rd President of the 
> > > U.S."
> > 
> > But even so, one might want to argue that "The 43rd President 
> > of the U.S."
> > is not George W. Bush.  Requiring a common, fixed denotation 
> > for all URI
> > references would eliminate this possibility.  (Unless, of 
> > course, you meant
> > that there was some sort of intensional denotation here.)
> 
> Not at all. As I've given examples before, if you want to talk
> about the denotation of a URI, you have to reify that URI and
> make statements about the URI, not the resource denoted by that
> URI.
> 
> You can't say 
> 
> <http://www.whitehouse.gov/#43> denotes "The 43rd President of the U.S."
> 
> to mean that the URI http://www.whitehouse.gov/#43 denotes the 43rd
> president of the US. What you've said above is that the resource
> denoted by the URI http://www.whitehouse.gov/#43 denotes the 43rd
> president of the US, or in other words, the 43rd president of the US
> denotes the 43 president of the US.

No, of course, you can't use URIs this way.  But I don't want to, and don't
have to.  Instead I could say

   <http://www.whitehouse.gov/#43> owl:sameAs <name:AlGore> .

which doesn't require reification or denotation relationships in the
language.

[...]

> > I completely disagree with this.  If you nail down the denotations of
> > everything, then why bother with the Semantic Web?  
> 
> Eh? Huh? URIs are atomic primitives of the semantic web which allow
> us to describe the *things* denoted by those URIs. The point of nailing
> down consistent unambiguous denotations is so that we can all talk 
> about the same *things* with consistency and clarity (or at least more
> consistency and clarity than natural language).

But people don't need to talk about the same things to be able to
communicate.  There does need to be some shared context, but this certainly
does not need to be a total context shared by all.

> I really wonder what kind of semantic web you are envisioning...

One that is more liberal than the one you appear to be envisioning.

> You seem rather to be wanting a semantic web to define the semantic web.
> You appear to want a framework below the semantic web for defining the atomic
> primitives used by the semantic web. Well, fine and good. Go for it.
> But until you provide it, the semantic web will have to operate on
> the presumption that URIs are fully opaque, globally unambiguous
> names for things and that a given URI always is *supposed* to mean
> the same thing (not that there is any guaruntee is actually will).

I'm not asking for this at all.  I even think that the currently-proposed
nature of the Semantic Web, as embodied in RDF and OWL, is capable of doing
much of this already.

> > It 
> > appears to me that
> > the benefits of the Semantic Web (over XML, for example) are 
> > intimately
> > involved with partial and conflicting information.
> 
> Sorry, but I will have to see a clear and motivating example of
> such a benefit. What you are suggesting sounds irrational to me.
>  
> Show me the code... Show me a use case... Show me...

Well most current Semantic Web code only works where the context is shared
in the way that you want.  I, however, am interested in building Semantic
Web applications that break out of this limitation.

> And note specifically (and I've tried to stress this before) that
> I differentiate between the denotation of a URI and knowledge
> expressed about the denoted resource using that URI.

I don't see a distinction here.

For example, suppose that we have two web pages http://a.ex/ containing
	<http://a.ex/john> rdf:type _:a .
	_:a owl:onProperty <http://c.ex/people#married> .
	_:a owl:maxCardinality "0"^^xsd:nonNegativeInteger .
and http://b.ex/ containing
	<http://a.ex/john> <http://c.ex/people#married> <http://b.ex/mary> .

What then is the denotation of <http://b.ex/mary>?  In particular, how is
http://a.ex/ supposed to fit this denotation into its view of the world.

> I agree that there can and will be disagreement between statements
> about resources denoted by URIs, but there should not be disagreement
> about the denotation of the URIs themselves. If there is, then 
> how do you even know that you are disagreeing about statements
> about a resource, if in fact, you are simply talking about
> different resources?

Maybe you won't even know that you are talking about ``different
resources'' and you won't care.  For example, you might disagree about who
is the current first lady without disagreeing where the first lady lives.

> Ambiguity in the SW is anathema, and will always be detrimental.
> 
> Yes, SW agents will have to deal with it more or less, but the
> less the better.
> 
> It is *never* going to be beneficial.
> 
> Though feel free to prove me wrong.

Ambiguity is difficult to deal with, agreed, and it is reasonable to try to
reduce it to the extent possible.  However, mandating that certain kinds of
ambiguity are not permissable, just means that one cannot deal with
situations where these kinds of ambiguity actually exist.  

[...]

> Patrick

peter
Received on Tuesday, 8 April 2003 13:53:49 GMT

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