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Re: owl:sameAs - Is it used in a right way?

From: Jim McCusker <mccusj@rpi.edu>
Date: Sat, 16 Mar 2013 12:37:40 -0400
Message-ID: <CAAtgn=QCy9eXDwNppkW11rRsr+pt3egEGK46bJiTqaa8Bq8YGQ@mail.gmail.com>
To: David Booth <david@dbooth.org>
Cc: Jeremy J Carroll <jjc@syapse.com>, Umutcan ŞİMŞEK <s.umutcan@gmail.com>, Kingsley Idehen <kidehen@openlinksw.com>, w3c semweb HCLS <public-semweb-lifesci@w3.org>
I'm not terribly interested in a Humpty Dumpty interpretation of the web of
data. That's part of the motivation for having global identifiers like
URIs/URLs. There's no point in merging ANY graphs under this view, since
you have no way of knowing if the referents are the same. I'm not saying
that people don't denote different things with the same URI, I'm saying
that, by using a URI that someone else controls, you are accepting their
denotation of it.

Jim


On Sat, Mar 16, 2013 at 12:30 PM, David Booth <david@dbooth.org> wrote:

> Hi Jim,
>
> You are in good company in thinking that a URI always denotes the same
> resource, because that is a widespread misconception.  (I call it Myth #1
> in http://dbooth.org/2010/**ambiguity/paper.html<http://dbooth.org/2010/ambiguity/paper.html>.)  But it simply is not true in the RDF semantics.
>
> The Architecture of the World Wide Web blithely states that "By design a
> URI identifies one resource":
> http://www.w3.org/TR/webarch/#**id-resources<http://www.w3.org/TR/webarch/#id-resources>
> But this is an architectural goal -- not the reality of RDF semantics.
> Although it is a good goal, and helpful as a guide to URI users, it turns
> out to be an oversimplification of reality.
>
> The RDF Semantics is very clear that a URI denotes one resource only in
> *one* interpretation of a *given* RDF graph:
> http://www.w3.org/TR/rdf-mt/#**interp<http://www.w3.org/TR/rdf-mt/#interp>
> But we do not have only one, giant, global RDF graph -- see Myth #2 -- we
> have *many* graphs.  And in general, a given RDF graph admits *many*
> satisfying interpretations.  The RDF semantics does not require that a URI
> denote the same resource in *different* graphs or in *different*
> interpretations of the same graph.
>
> Thus, although as an architectural goal we would *like* a URI to always
> denote the same resource, the reality is that a URI can -- and often does
> -- denote *different* resources in different graphs, and this can cause
> inconsistencies when graphs are merged, as illustrated in Figure 26:
> http://dbooth.org/2010/**ambiguity/paper.html#**inconsistent-merge<http://dbooth.org/2010/ambiguity/paper.html#inconsistent-merge>
>
> That is precisely why it is helpful to keep different perspectives in
> different graphs, as Jeremy suggested.
>
> David
>
>
> On 03/16/2013 01:08 AM, Jim McCusker wrote:
>
>> David,
>>
>> The problem with this is that by definition, URIs ALWAYS denote the same
>> resource. If there is doubt that you might be denoting something other
>> than what a resource is, you should be defining your own resource.
>>
>> Jim
>>
>>
>> On Sat, Mar 16, 2013 at 12:35 AM, David Booth <david@dbooth.org
>> <mailto:david@dbooth.org>> wrote:
>>
>>     Hi Umutcan,
>>
>>     You have indeed stumbled on a deep question, and I think Jeremy's
>>     suggestion is exactly right.  This paper on "Resource Identity and
>>     Semantic Extensions:
>>     Making Sense of Ambiguity" illustrates how owl:sameAs works in RDF
>>     semantics:
>>     http://dbooth.org/2010/__**ambiguity/paper.html#sameAs<http://dbooth.org/2010/__ambiguity/paper.html#sameAs>
>>
>>     <http://dbooth.org/2010/**ambiguity/paper.html#sameAs<http://dbooth.org/2010/ambiguity/paper.html#sameAs>
>> >
>>
>>     There are two keys to understanding owl:sameAs.  One is to answer
>>     the question: what RDF graph are you considering?  The other is to
>>     understand that the same URI may denote different things in
>>     different RDF graphs.  It is only when RDF statements are in the
>>     *same* graph that the RDF semantics requires the URI to denote the
>>     same resource.  That is why the question of what graph you are
>>     considering is crucial, and why Jeremy suggested keeping the
>>     different perspectives in different graphs.
>>
>>     FYI, the above paper also explains how you can "split" the identity
>>     of an RDF resource if you need to merge RDF graphs that use the same
>>     URI in contradictory ways.
>>
>>     David
>>
>>
>>
>>     On 03/15/2013 02:29 PM, Jeremy J Carroll wrote:
>>
>>         I did not find this a rookie question at all.
>>
>>         This seems to get to the heart of some of the real difficult
>>         issues in Semantic Web.
>>
>>         My perspective is different from yours, and a resource
>>         description that I author is a description of the resource from
>>         my perspective; a resource description that you author is a
>>         description from your perspective.
>>
>>         If I have some detailed application that depends in some subtle
>>         way on my description, I may want to ignore your version; on the
>>         other hand, a third party might want to use both of our points
>>         of view.
>>
>>         One way of tacking this problem is to have three graphs for this
>>         case:
>>
>>         Gj, Gu, G=
>>
>>         Gj contains triples describing my point of view
>>         Gu contains triples describing your point of view
>>         G= contains the owl:sameAs triples
>>
>>         Then, in some application contexts, we use Gj, sometimes Gu, and
>>         sometimes all three.
>>
>>         Jeremy
>>
>>
>>
>>
>>         On Mar 15, 2013, at 11:02 AM, Umutcan ŞİMŞEK
>>         <s.umutcan@gmail.com <mailto:s.umutcan@gmail.com>> wrote:
>>
>>             Thanks for the quick answer : )
>>
>>             So this issue is that subjective for contexts which allows
>>             to use owl:sameAs to link resources  if they are not
>>             semantically even a little bit related in real world?
>>
>>             Sorry if I'm asking too basic questions. I'm still a rookie
>>             at this :D
>>
>>             Umutcan
>>
>>
>>             On 15-03-2013 19:38, Kingsley Idehen wrote:
>>
>>                 On 3/15/13 1:05 PM, Umutcan ŞİMŞEK wrote:
>>
>>                     My question is, does LODD use owl:sameAs properly?
>>                     For instance, are those two resources,
>>                     dbpedia:Metamizole and drugbank:DB04817 (code for
>>                     Metamizole), really identical? Or am I getting the
>>                     word "property" in the paper wrong?
>>
>>                 The question is always about: do those URIs denote the
>>                 same thing? Put differently, do the two URIs have a
>>                 common referent?
>>
>>                 ## Turtle ##
>>
>>                 <#i> owl:sameAs <#you>.
>>
>>                 ## End ##
>>
>>                 That's a relation in the form of a 3-tuple based
>>                 statement that carries entailment consequences for a
>>                 reasoner that understand the relation semantics. Through
>>                 some "context lenses" the statement above could be
>>                 accurate, in others totally inaccurate.
>>
>>                 Conclusion, beauty lies eternally in the eyes of the
>>                 beholder :-)
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> --
>> Jim McCusker
>> Programmer Analyst
>> Krauthammer Lab, Pathology Informatics
>> Yale School of Medicine
>> james.mccusker@yale.edu <mailto:james.mccusker@yale.**edu<james.mccusker@yale.edu>>
>> | (203) 785-4436
>>
>> http://krauthammerlab.med.**yale.edu <http://krauthammerlab.med.yale.edu>
>>
>> PhD Student
>> Tetherless World Constellation
>> Rensselaer Polytechnic Institute
>> mccusj@cs.rpi.edu <mailto:mccusj@cs.rpi.edu>
>> http://tw.rpi.edu
>>
>


-- 
Jim McCusker
Programmer Analyst
Krauthammer Lab, Pathology Informatics
Yale School of Medicine
james.mccusker@yale.edu | (203) 785-4436
http://krauthammerlab.med.yale.edu

PhD Student
Tetherless World Constellation
Rensselaer Polytechnic Institute
mccusj@cs.rpi.edu
http://tw.rpi.edu
Received on Saturday, 16 March 2013 16:38:25 UTC

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