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Re: [Linking-open-data] Terminology Question concerning Web Architecture and Linked Data

From: Kingsley Idehen <kidehen@openlinksw.com>
Date: Sun, 22 Jul 2007 11:37:22 -0400
Message-ID: <46A379B2.10702@openlinksw.com>
To: Linking Open Data <linking-open-data@simile.mit.edu>
CC: Mark Baker <distobj@acm.org>, semantic-web@w3.org, www-tag@w3.org

Chris Bizer wrote:
> Hi Mark,
> interesting point of view.
>> [...]
>>> Question 1: According to the terminology of the Architecture of the WWW
>>> document [4] are all these URIs aliases for the same non-information
>>> resource (our current view) or are they referring to different resources?
>>> Does the TAG finding "On Linking Alternative Representations To Enable
>>> Discovery And Publishing " [5] about generic and specific resources apply
>>> here, meaning that the URIs 1,2,3,5 refer to different specific
>>> non-information resources that are related to one generic non-information
>>> resource?
>> IMO, those URIs identify different resources.  I say this because they
>> all return different representations when I dereference them.  If they
>> identified the same resource then their representations would be
>> identical (see Roy's definition of resource in his REST dissertation).
>> The tricky bit here is to remember to account for agency; to recognize
>> that although dbpedia.org uses URI #1 to identify Tim, from a third
>> party's POV it identifies dbpedia.org's *view* of Tim.
> But I think I prefer to follow Dan's view on this 
> (http://lists.w3.org/Archives/Public/semantic-web/2007Jul/0102.html), as by 
> seeing them as URI aliases you get a nice straight architecute that 
> harmonizes with 303 redirects, content negotiation and alike.
> As you said, if they were different resources you run into problems with 
> agency. Seeing them as URI aliases solves these problems as we tried to 
> explain in our Linked Data tutorial 
> (http://sites.wiwiss.fu-berlin.de/suhl/bizer/pub/LinkedDataTutorial/#aliases). 
> Quote:
> "Within an open environment like the Web it often happens that multiple 
> information providers talk about the same non-information resource, for 
> instance a geographic location or a famous person. As they do not know about 
> each other, they introduce different URIs for identifying the same 
> real-world object. For instance: DBpedia a data source providing information 
> that has been extracted from Wikipedia uses the URI 
> http://dbpedia.org/resource/Berlin to identify Berlin. Geonames is a data 
> source providing information about millions of geographic locations uses the 
> URI http://sws.geonames.org/2950159 to identify Berlin. As both URIs refer 
> to the same non-information resource, they are called URI aliases. URI 
> aliases are common on the Web of Data, as it can not realistically be 
> expected that all information providers agree on the same URIs to identify a 
> non-information resources. URI aliases provide an important social function 
> to the Web of Data as they are dereferenced to different descriptions of the 
> same non-information resource and thus allow different views and opinions to 
> be expressed. In order to still be able to track that different information 
> providers speak about the same non-information resource, it is common 
> practice that information providers set owl:sameAs links to URI aliases they 
> know about. This practice is explained in Section 5 in more detail."
> Cheers
> Chris
>>> Question 3: Depending on the answer to question 1, is it correct to use
>>> owl:sameAs [6] to state that http://www.w3.org/People/Berners-Lee/card#i 
>>> and
>>> http://dbpedia.org/resource/Tim_Berners-Lee refer to the same thing as it 
>>> is
>>> done in Tim's profile.
>> No.  AIUI, owl:sameAs is a very strong predicate which declares
>> subject and object to be the same resource.  I only foresee it being
>> used by a publisher to declare equivalence of their own URIs, because
>> being able to guarantee equivalence requires a very tight degree of
>> control over them (i.e. be able to serve identical representations for
>> all time).
>> Mark.
>> -- 
>> Mark Baker.  Ottawa, Ontario, CANADA.         http://www.markbaker.ca
>> Coactus; Web-inspired integration strategies  http://www.coactus.com


What is the expected result for a SPARQL Query against Tim's Structured 
Data Resource URI (aka Non Informational Resource): 

The generic query:

select distinct *
from <http://www.w3.org/People/Berners-Lee/card#i>
where {<http://www.w3.org/People/Berners-Lee/card#i> ?s ?p}

The query as executed using Virtuoso's SPARQL processor with owl:sameAs 
inferencing enabled:

define input:same-as "yes"
FROM <http://www.w3.org/People/Berners-Lee/card#i>
  <http://www.w3.org/People/Berners-Lee/card#i> ?s ?p .

The answer to the above is somehow getting drowned in the conversation. 
The answer is very important since Tim's expectations of "owl:sameAs" in 
this scenario are crystal clear to me.

Note: I provided my answer at the start of this whole discussion. I am 
interested in yours as it is unclear to me if there is any agreement re. 
this matter.


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Kingsley Idehen	      Weblog: http://www.openlinksw.com/blog/~kidehen
President & CEO 
OpenLink Software     Web: http://www.openlinksw.com
Received on Sunday, 22 July 2007 15:37:36 UTC

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