W3C home > Mailing lists > Public > www-tag@w3.org > July 2007

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

From: Chris Bizer <chris@bizer.de>
Date: Sun, 22 Jul 2007 22:57:03 +0200
Message-ID: <003901c7cca2$db05d7f0$c4e84d57@named4gc1asnuj>
To: <kidehen@openlinksw.com>, "Linking Open Data" <linking-open-data@simile.mit.edu>
Cc: "Mark Baker" <distobj@acm.org>, <semantic-web@w3.org>, <www-tag@w3.org>

Hi Kingsley,

I think SPARQL queries and URI dereferencing according to AWWW are two 
seperate things.

When a agent dereferences http://www.w3.org/People/Berners-Lee/card#i it 
gets Tim's foaf profile and that's it.

The agent is free to look into the data afterwards and search for owl:sameAs 
statements. It is also free to dereference all URIs that it finds within 
these statements. It is free to do inference or URI smushing over the data. 
And it is free to execute SPARQL queries over the dereferenced data. A good 
agent will do all this. But according to AWWW it does not have to and it can 
also do other things if it likes.

So I think there is no single answer to your question "What is the expected 
result for a SPARQL Query against Tim's Structured
 Data Resource URI (aka Non Informational Resource)".



Chris Bizer
Freie Universitšt Berlin
+49 30 838 54057
----- Original Message ----- 
From: "Kingsley Idehen" <kidehen@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>
Sent: Sunday, July 22, 2007 5:37 PM
Subject: Re: [Linking-open-data] Terminology Question concerning Web 
Architecture and Linked Data

> 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
> Chris,
> What is the expected result for a SPARQL Query against Tim's Structured 
> Data Resource URI (aka Non Informational Resource): 
> http://www.w3.org/People/Berners-Lee/card#i
> 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.
> Kingsley
>> _______________________________________________
>> Linking-open-data mailing list
>> Linking-open-data@simile.mit.edu
>> http://simile.mit.edu/mailman/listinfo/linking-open-data
> -- 
> Regards,
> Kingsley Idehen       Weblog: http://www.openlinksw.com/blog/~kidehen
> President & CEO OpenLink Software     Web: http://www.openlinksw.com
Received on Sunday, 22 July 2007 20:57:13 UTC

This archive was generated by hypermail 2.4.0 : Friday, 17 January 2020 22:56:16 UTC