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to-what-does-a-uri-refer

From: David Booth <david@dbooth.org>
Date: Mon, 08 Nov 2010 14:12:51 -0500
To: AWWSW TF <public-awwsw@w3.org>
Message-ID: <1289243571.5492.19436.camel@dbooth-laptop>
Hi Jonathan,

Some comments on your blog entry at
http://odontomachus.wordpress.com/2010/11/08/to-what-does-a-uri-refer/ 

> We can use one URI to refer to different things depending
> on context? – You can try, but there are some problems
> with trying to revoke the “U” in “URI”. One is
> that computers and programmers get things wrong, and the
> likelihood that the context might be misread makes for a
> fragile system. Another is that context sensitivity is a
> threat to polymorphism (functions that are generic across
> domains) and to interoperability (combining functions
> across domains).

But due to ambiguity of resource identity, a form of
context dependency is what happens all the time, even
if we don't think of it as an intended context dependency.  

For example, suppose you have a URI X, and <X> denotes 
one resource in RDF graph A, but a different resource
in RDF graph C.  Presumably in some sense this would
be considered a context dependency.  Right?

But this is *normal* in the world of RDF, because: (a)
the original definition of <X> -- a definition that is
shared by both graphs A and C -- is ambiguous; (b) graphs
that use X further constrain its interpretations, but in
different ways; and (c) ambiguity of resource identity
is inescapable, no matter how well we try to write our
definitions.

This is illustrated as graphs A and C in
http://dbooth.org/2010/ambiguity/paper.html#inconsistent-merge 
That document as a whole at
http://dbooth.org/2010/ambiguity/paper.html
provides a pretty clear explanation of how ambiguity works
in RDF semantics.

> [ . . . ]
> 
> We can say a URI refers to an ontological chimera
> of a web page and something else? – That is,
> http://dbpedia.org/page/Paris might simultaneously have
> both authors and a population? 

Yes!  As long as the definitions of web page and city are
not mutually exclusive.  The point is that it is generally
not possible to nail down the identity of resource without
ambiguity.  This is neatly captured in the RDF
Semantics by the notion of interpretations:
http://www.w3.org/TR/rdf-mt/#interp
[[
It is usually impossible to assert enough in any language
to completely constrain the interpretations to a single
possible world, so there is no such thing as 'the' unique
interpretation of an RDF graph.
]]

And, as explained at
http://dbooth.org/2007/splitting/ 
the ambiguity between a city and its web page is not
fundamentally different than other ambiguity of resource
identity.  We just have to get used to ambiguity
anyway.  


-- 
David Booth, Ph.D.
Cleveland Clinic (contractor)
http://dbooth.org/

Opinions expressed herein are those of the author and do not necessarily
reflect those of Cleveland Clinic.
Received on Monday, 8 November 2010 19:13:20 GMT

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