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RE: web proper names

From: David Menendez <zednenem@psualum.com>
Date: Tue, 21 Sep 2004 21:27:01 -0400
To: Hamish Harvey <david.harvey@bristol.ac.uk>
Cc: www-rdf-interest@w3.org
Message-id: <r02010200-1035-816B99D60C3611D9B4B0000393758032@[192.168.2.44]>

Hamish Harvey writes:

> 
> This debate has caused a decided shift in my understanding of this
> issue. There follows a summary. Comments and flames the very purpose
> of posting. Am I missing the point? Making some rudimentary mistake?

Your interpretation looks pretty similar to mine.

Here's another scenario that helped shape my thinking on the subject.
Lets say we have two URIs that identify the same resource.

    <http://example.com/thing/1> owl:sameAs <http://example.org/obj/58>.

Effectively, that means that anywhere we see
<http://example.com/thing/1> in an RDF graph, we can replace it with
<http://example.org/obj/58>, and vice versa.

However, it is probably the case that dereferencing those URIs gives
different pages.

    _:P1 ex:resultOfDereferencing 
            "http://example.com/thing/1"^^xsd:anyURI.
    _:P2 ex:resoltOfDereferencing 
            "http://example.org/obj/58"^^xsd:anyURI.

If we tried to represent this information like so:

    _:P1 ex:resultOfDereferencing <http://example.com/thing/1>.
    _:P2 ex:resultOfDereferencing <http://example.org/obj/58>.

we wouldn't be able to distinguish the sources of _:P1 and _:P2.


Alternately, consider that web pages can change even if the resources
their URIs identify do not:

    <http://example.com/> a foaf:Document
        ; dc:title "Home page of Example.com"
        .
    
    _:P3 ex:resultOfDereferencing "http://example.com/"^^xsd:anyURI
        ; ex:retrievalDate "2004-09-20"^^xsd:date
        ; dc:creator "Joe Example"
        .
    
    _:P4 ex:resultOfDereferencing "http://example.com/"^^xsd:anyURI
        ; ex:retrievalDate "2004-09-21"^^xsd:date
        ; dc:creator "Fred Hypothetical"
        .

> Assuming we hadn't already made that commitment, however, we would be
> free to use this URI in its "natural" (read -- intuitive to some)
> role, as indicating the document (probably not as natural as it
> seems, though, as explored in tortuous detail in the Functional
> Requirements for Bibliographic Records recommendation [1] which talks
> of works, expressions, manifestations, and items).
> 
> [1] http://www.oclc.org/research/projects/frbr/default.htm

Very true. I suspect most web pages probably fall in the Work or
Expression categories, depending on how much they change over time.

> It follows then that no software is allowed to treat a (URI qua
> symbol) as it appears in an RDF graph as anything other than a
> totally opaque symbol. It is *only* if it is explicitly specified
> that a URI (or bnode) indicates some specific retrievable resource
> that it is valid to go beyond the "inaccessible indicated thing"
> level of interpretation.

On the other hand, if a user can dereference a URI to see if the result
sheds any light on the URI's meaning, there's no reason that a software
agent couldn't do the same.

-- 
David Menendez <zednenem@psualum.com> | "In this house, we obey the laws
<http://www.eyrie.org/~zednenem>      |        of thermodynamics!"
Received on Wednesday, 22 September 2004 01:27:05 GMT

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