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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 12:43:57 -0400
Message-ID: <CAAtgn=Tr9W8-8RaOzGWvcYkDm_=-N-qyBmQEK_76eNC5wyxfhQ@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 see "A URI denotes only one resource" as a rule of the game that makes it
far more interesting than if we don't accept that rule. If I find that
someone is violating that rule, I'll kick them out of my game (exclude
their graph).

Jim


On Sat, Mar 16, 2013 at 12:37 PM, Jim McCusker <mccusj@rpi.edu> wrote:

> 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
>



-- 
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 16:44:40 UTC

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