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Re: synonym URIs (Re: homonym URIs Re: What if an URI also is a URL)

From: Chris Bizer <chris@bizer.de>
Date: Wed, 13 Jun 2007 08:59:39 +0200
Message-ID: <001001c7ad88$884fff10$c4e84d57@named4gc1asnuj>
To: "Tanel Tammet" <tammet@staff.ttu.ee>, "Pat Hayes" <phayes@ihmc.us>
Cc: "Sandro Hawke" <sandro@w3.org>, <semantic-web@w3.org>, <timbl@w3.org>, "Linking Open Data" <linking-open-data@simile.mit.edu>

Hi Tanel,

> Since the synonyms of the above kind are - obviously -  extremely 
> widespread, should not there be a standardised mechanism for equality 
> axioms in the sem web world? For example, extending rdfs to to  rdfse  by 
> adding the rdfse:equal predicate with a classical semantics?
>
> Once we start using the rdfse:equal and state things like
>
> http://www.ihmc.us/users/phayes/PatHayes.html rdfse:equal 
> http://www.ttu.ee/it/PatHayes.html

I completely agree with you that synonym URIs will be widespread on the 
Semantic Web. Therefore,

- the idea of having a single URI that everybody uses to identify a concept 
will not work and we should just forget about it
- explicit statements about the equivialence of URIs are an important part 
of the glue that hold the Semantic Web together.

These points can nicely be proven with experience from the Linking Open Data 
project 
(http://esw.w3.org/topic/SweoIG/TaskForces/CommunityProjects/LinkingOpenData).

Take Tim Berners-Lee as an example. He has assigned a URI to himself:
http://www.w3.org/People/Berners-Lee/card#i

Note that his URI identifies him as an real-world resource/concept and not 
the Web page/RDF file about him.

There are several other data sources in the network that provide information 
about Tim and assign different URIs to him (again as a real-world concept). 
For example:

DBpedia, which calls him
http://dbpedia.org/resource/Tim_Berners-Lee

The RDF Book Mashup, which provides information about his books and calls 
him
http://www4.wiwiss.fu-berlin.de/bookmashup/persons/Tim+Berners-Lee

The DBLP database, which provides information about his papers and calls him
http://www4.wiwiss.fu-berlin.de/dblp/resource/person/100007

In oder to be able to integrate information about him from different 
sources, we rely on explicit equivialence statements using the owl:sameAs 
property (instead of rdfse:equal as you proposed).

If you look into Tim's FOAF profile at 
http://www.w3.org/People/Berners-Lee/card, you will see that it contains two 
owl:sameAs statements, claiming that he is equal to
http://www4.wiwiss.fu-berlin.de/bookmashup/persons/Tim+Berners-Lee and 
http://www4.wiwiss.fu-berlin.de/dblp/resource/person/100007.

You can browse along these links into the other data sources by looking at 
Tim's profile with DISCO (link below) and clicking on the URI in the 
owl:sameAs rows.

http://www4.wiwiss.fu-berlin.de/rdf_browser/?browse_uri=http%3A%2F%2Fwww.w3.org%2FPeople%2FBerners-Lee%2Fcard%23i

Tim has added these links manually to his FOAF profile. When we start 
interlinking larger data sources, manually set links will not scale to well 
and therefore automated equivialence mining and record linkage comes into 
the picture.

Look for instance on the DBpedia website http://dbpedia.org/docs/. There you 
will find download for around 100 000 owl:sameAs links that connect entities 
from the DBpedia dataset with entities within other databases like 
Musicbrainz, Geonames, DBLP and so on.

I think record linkage will be one of the most important topics for the 
Semantic Web in the future and we are collecting material about it at 
http://esw.w3.org/topic/TaskForces/CommunityProjects/LinkingOpenData/EquivalenceMining

See also Yves post about linking Jamendo to Musicbrainz
http://blog.dbtune.org:80/post/2007/06/11/Linking-open-data:-interlinking-the-Jamendo-and-the-Musicbrainz-datasets

Cheers

Chris

--
Chris Bizer
Freie Universitšt Berlin
+49 30 838 54057
chris@bizer.de
www.bizer.de

----- Original Message ----- 
From: "Tanel Tammet" <tammet@staff.ttu.ee>
To: "Pat Hayes" <phayes@ihmc.us>
Cc: "Sandro Hawke" <sandro@w3.org>; <semantic-web@w3.org>; <timbl@w3.org>
Sent: Wednesday, June 13, 2007 7:08 AM
Subject: synonym URIs (Re: homonym URIs Re: What if an URI also is a URL)


>
> Pat Hayes wrote:
>> You are begging the question. Suppose an ontology asserts
>>
>> ex:Venus rdf:type ex:AstronomicalBody .
>>
>> Now, what ties that object URI to the actual concept of being an 
>> astronomical body? And so on for all the other URIs in all the other 
>> OWL/RDF ontologies. The best you can do is to appeal to the power of 
>> model theory to sufficiently constrain the interpretations of the entire 
>> global Web of formalized information. But that argument from Herbrand's 
>> theorem (basically, if it has a model at all then it has one made 
>> entirely of symbols) applies just as well no matter how large the 
>> ontology is.
>>
>> The only way out of this is to somewhere appeal to a use of the symbolic 
>> names - in this case, the IRIs or URIrefs - outside the formalism itself, 
>> a use that somehow 'anchors' or 'grounds'  them to the real world they 
>> are supposed to refer to. If we all assume that English words are so 
>> grounded (not a bad assumption) then this can be done in principle by 
>> using the URI in English sentences or to other kinds of representation 
>> which are widely accepted as real-world identifiers, like SS numbers or 
>> facial images. I did all three in
>>
>> http://www.ihmc.us/users/phayes/PatHayes.html
>>
>> If the TAG said this somewhere, and recommended how to do it, that would 
>> be great.
> Approaching the same issue from an opposite direction:
>
> There is not much hope of "guaranteeing" that 
> http://www.ihmc.us/users/phayes/PatHayes.html will always automagically 
> denote the actual Pat Hayes (despite the convincing suggestions on the 
> referred html page).
>
> For similar reasons people will use their own URIs to denote Pat Hayes. I 
> could, say, write a similar html page for Pat to, say, 
> http://www.ttu.ee/it/PatHayes.html, and start using that in my formalism 
> and software. After learning about the existence of 
> http://www.ihmc.us/users/phayes/PatHayes.html, I'd probably want to 
> incorporate other formalisms and systems into my own. The only real/proper 
> way to do this would be stating the synonymy as honest first order 
> equality:
>
> http://www.ttu.ee/it/PatHayes.html=http://www.ihmc.us/users/phayes/PatHayes.html
>
> First, this would be correct _only_ in case  when both URI-s above
>
> - are not treated as strings (these two URI strings are obviously 
> different)
> - are not treated as web pages (the referred web pages as strings will - 
> probably - be also different)
>
> Additionally, we will need machinery for handling equality. In simple 
> cases like synonymous URIs the decidability of formalisms can be preserved 
> even in the presence of equality, hence there are no strong reasons for 
> dismissing the equality on purely practical grounds.
>
> Since the synonyms of the above kind are - obviously -  extremely 
> widespread, should not there be a standardised mechanism for equality 
> axioms in the sem web world? For example, extending rdfs to to  rdfse  by 
> adding the rdfse:equal predicate with a classical semantics?
>
> Once we start using the rdfse:equal and state things like
>
> http://www.ihmc.us/users/phayes/PatHayes.html rdfse:equal 
> http://www.ttu.ee/it/PatHayes.html
>
> we might sometimes want a way to state that the _actual html strings_ 
> referred to by the URI's are equal. For example, if I'd copy the original 
> Pat page to http://www.ttu.ee/it/copyOfOriginalPageOfPatHayes.html, I 
> might want to state something like
>
> rdfse:urlpagestring(http://www.ttu.ee/it/PatHayes.html)=rdfse:urlpagestring(http://www.ihmc.us/users/phayes/PatHayes.html)
>
> or at least
>
> (http://www.ttu.ee/it/PatHayes.html rdfse:urlpagestring ?X)  & 
> (http://www.ihmc.us/users/phayes/PatHayes.html rdfse:urlpagestring ?Y) =>
> ?X rdfse:equal ?Y
>
> The presence of rdfse:urlpagestring and rdfse:equal in a language would 
> make it easier to avoid the permanent confusion between the actual Pat 
> Hayes and his web page.
>
> We could even axiomatize the difference of objects and their web page 
> strings as
>
> forall ?X.  not(?X rdfse:equal rdfse:urlpagestring(?X))
>
> formally "solving" the question once and for all :)
>
> Tanel Tammet
>
>
>
> 
Received on Wednesday, 13 June 2007 07:00:34 UTC

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