Re: Meaning of URIRefs

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Date: Mon, 28 Oct 2002 11:21:50 -0500 (EST)
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To: <www-rdf-interest@w3.org>
Subject: Re: Meaning of URIRefs

Maybe it helps to distinguish two cases:
a) referring to a name
b) referring to a model/ontology (including names and statements about
their relations)

Obviously both cases are useful.
To say 'Berlin was founded in 1735' (which is wrong), I don't need to
take any model into account, and getting access to the name 'Berlin'
only
with an attached model may even get me into trouble (as others have
pointed
out already). Note that quoting the name won't help here because I want
to
establish a fact about Berlin, not about the name 'Berlin'.
I assume that Sandro wants to use the 'definitional' statements to
ensure
that the owner of the name 'Berlin' and me refer to the same Berlin
(e.g. not to Berlin, NH, USA). IMHO this can't be guaranteed within the
SW, but only by human convention. My guess ist that as we humans
nowadays
'know' that www.ibm.org is IBMs web site, we will 'know' that
www.geographicnames.org/germany/berlin (or whatever URI) denotes
the city Berlin in Germany.
Therefore I think it should be possible to use a name without being
forced to assert anything stated by the name's owner.

OTOH it is also useful to say 'Spot is a Dog, according to the
animal classification system at www.allmyanimals.org'. Here I do not
only want to use a name, but refer to the complete ontology.
I agree with Sandro that there are ontologies where it doesn't even make

sense to use terms from that ontology without asserting the truth of the
whole ontology.

Both ways of using a name have their place and should be supported
within the SW.


- Wolf



 > -----Ursprüngliche Nachricht-----
 > Von: www-rdf-interest-request@w3.org
 > [mailto:www-rdf-interest-request@w3.org] Im Auftrag von Geoff Chappell
 > Gesendet: Sonntag, 27. Oktober 2002 23:10
 > An: 'Sandro Hawke'
 > Cc: www-rdf-interest@w3.org
 > Betreff: RE: Meaning of URIRefs
 >
 >
 >
 >
 >
 > > -----Original Message-----
 > > From: www-rdf-interest-request@w3.org [mailto:www-rdf-interest-
 > > request@w3.org] On Behalf Of Sandro Hawke
 > > Sent: Friday, October 25, 2002 10:11 AM
 > > To: Peter F. Patel-Schneider
 > > Cc: www-rdf-interest@w3.org
 > > Subject: Re: Meaning of URIRefs
 > >
 > >
 > >
 > > In a message sent to www-rdf-comments that was intented for
 > this list,
 > > Peter F. Patel-Schneider wrote:
 > > >
 > > > [A discussion on whether using foo#bar commits one to the
 > information
 > > > available at foo, moved from www-rdf-comments.]
 > > >
 > > > Sandro's position is that the use of a URI reference
 > commits one to
 > the
 > > > entirety of the information in the document that can be found by
 > > > dereferencing the non-fragment part of the URI reference.
 > > >
 > > > The basic problem that I have with this position is that
 > I feel that
 > it
 > > > poses a significant bar to communication.
 > > >
 > > > To pick a very mundane example, suppose that company A has a URI,
 > > > http://A.com.ex/invoice.rdf, whose contents consist of invoices.
 > > >
 > > > The first problem with Sandro's position is that company A has a
 > serious
 > > > dilemma in placing identifiers for other companies in these
 > invoices.
 > > The
 > > > only reasonable kind of identifier for another company,
 > say company
 > B,
 > > > would be a URI reference from a URI controlled by company B.  But
 > the
 > > > simple use of this URI reference, say http://B.com.ex#B, commits
 > company
 > > A
 > > > to everything said on http://B.com.ex.  It is certain that
 > > http://B.com.ex
 > > > is going to make disputable claims about company B, which
 > company A
 > does
 > > > not want to commit to.
 > > >
 > > > The second problem with Sandro's position is that other companies
 > are
 > > going
 > > > to have problems in disputing the invoices of company A.  The only
 > way
 > > they
 > > > have to refer to these invoices is via URI references taken from
 > > > http://A.com.ex/invoice.rdf, but just the use of one of these URI
 > > > references commits the other company to the information in
 > > > http://A.com.ex/invoice.rdf, which is going to include
 > the fact that
 > the
 > > > invoice in question is a valid invoice.
 > > >
 > > > I don't see any way around these dilemmas without denying Sandro's
 > > > position.
 > >
 > > The way around these problems is to split definitional content and
 > > general content into different documents.  The definitional content
 > > about the invoice would include information like the invoice number
 > > and an identifier for the parties issuing the invoice.  The general
 > > content about the invoice would include identifying the goods and
 > > services rendered, their prices, etc.  A dispute over the
 > definitional
 > > content would have quite a different quality than a dispute over the
 > > general content; it would probably be resolved by finding the right
 > > invoice.
 > >
 > > Similarly, the definitional information about company B should only
 > > make claims which serve to identify company B, such as its official
 > > (name, jurisdiction) pair.  Additional information (such as its
 > > dispute resolution policies) belong elsewhere.
 > >
 > > If companies A and B choose not to offer such unencumbered
 > > definitional content, then others are free to do so.  In the worst
 > > case, where no one is willing to publish such a definition, one can
 > > always fall back to doing it with a bNode inside your own document.
 > > This fallback approach requires reasoning about inverse functional
 > > properties instead of just string-equality, but it is already in use
 > > [1] [2].
 > >
 > > In situations where the definitions are more complex, and many terms
 > > are interrelated (such as with OWL, DC, CC, RSS, ... basically any
 > > non-trivial ontology) this bNode approach is less feasible.  Then it
 > > becomes more important to have a stable URI for good definitional
 > > content, but it's also much more likely because the
 > ontology creators
 > > are likely to understand this issue better.
 > >
 > >     -- sandro
 > >
 > > [1] http://www-106.ibm.com/developerworks/xml/library/x-foaf2.html
 > > [2]
 > http://lists.w3.org/Archives/Public/www-rdf-logic/2001Sep/0004.html
 >
 > Even if we are not _required_ to commit to someone else's statements
 > about a resource by using their name for it, it seems to me we
 > effectively will if the statements are made by an authoritative source
 > that many people trust. For example, if we use a trusted web
 > encyclopedia's URI for a resource to refer to that resource
 > and someone
 > merges our statements with statements from their other trusted sources
 > (including the encyclopedia), we will have ended up agreeing
 > in a way to
 > all authoritative statements about that resource (i.e. by
 > using a common
 > name for something we buy into all aspects of its common meaning). In
 > fact it may be very difficult to not do so. Inverse functional
 > properties, cardinality restrictions, etc. may force a well-connected
 > reasoner to infer that the URI we use for something refers to
 > the exact
 > same object that the authoritative source calls by a
 > different name (and
 > so our URI and the authoritative URI can be used interchangeably).
 >
 > I wonder if it might be handy to have a way of scoping the
 > consequences
 > of our use of a name. Instead of an inverse functional property being
 > used to infer the identity of objects, perhaps it could sometimes just
 > be used to infer equality under a set of properties. For
 > example, say we
 > use a bNode to refer to a certain president and a property such as
 > http://www.us-presidents.org/justTheFacts#number (which is specified
 > somehow so that any two resources with the same value of this property
 > have the same values for all other properties that begin
 > http://www.us-presidents.org/justTheFacts#). Our bNode
 > wouldn't inherit
 > the properties/values from
 > http://www.us-presidents.org/andNowSomeOpinions or other
 > namespaces/documents that are attributed to other URIs with the same
 > value of #number. Make any sense?
 >
 > --Geoff Chappell
 >
 >

Received on Monday, 28 October 2002 15:49:00 UTC