- From: David Booth <david@dbooth.org>
- Date: Sat, 16 Mar 2013 12:30:54 -0400
- To: Jim McCusker <mccusj@rpi.edu>
- 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>
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 .) 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 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 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 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> > > 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> | (203) 785-4436 > 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
Received on Saturday, 16 March 2013 16:31:21 UTC