W3C home > Mailing lists > Public > www-rdf-interest@w3.org > March 2004

Re: a bnode URI scheme?!

From: Adam Souzis <adam-l@souzis.com>
Date: Thu, 11 Mar 2004 20:07:15 -0800
Message-ID: <40513773.2060207@souzis.com>
To: Sandro Hawke <sandro@w3.org>
Cc: www-rdf-interest@w3.org

Yes of course that is not true but irrelevant. I am talking about RDF's, 
not OWL's, semantics -- in RDF the meaning of URIs are intensional -- 
you need a higher level intepretation theory -- like OWL -- to determine 
equivalence. Thus there is no way in RDF model theory to assert 
something like

<a> owl:differentFrom <d> or <a> owl:sameAs <d> 

But bNodes, as existential variables, are extensional -- if they weren't 
the graph equivalency rule wouldn't make sense, nor could you do simple 
entailment.

You could say, who cares, I'm only interested in a (particular) OWL 
interpretation -- well, I address whether that approach is desirable in 
my original email.

Yes, bNodes are a real pain to reason about, but I'm not sure that implies RDF tool developers should avoid trying to understand them.

-- adam

Sandro Hawke wrote:

>>Consider the address bnode example in the RDF Primer 
>>(http://www.w3.org/TR/2004/REC-rdf-primer-20040210/#structuredproperties).
>>There may be times when you want to reference that address externally 
>>(e.g. from another model) but the common sense approach to enable that 
>>by just replacing the bNode with a URI reference has a couple of problems:
>>* it changes the meaning of the model: bNodes serve as existential 
>>variables -- if you replace two distinct bNodes x and y with 2 different 
>>URIs you are adding information to the model: because there is nothing 
>>in the model that says x and y might not be equal but the two URIs that 
>>replace are indeed not equal (since RDF uses intensional semantics for 
>>URIs).
>>    
>>
>
>Not true.   
>
>I think you're saying 
>
><a> <b> <c>.
><d> <e> <f>.
>
>entails
>
><a> owl:differentFrom <d>.
>
>... but I really don't think that's the case.  Can you find some
>supporting text?
>
>(My recommendation: bNodes are a real pain to reason about, so avoid
>them unless doing so is an even bigger pain.)
>
>       -- sandro
>  
>
Received on Thursday, 11 March 2004 23:07:02 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 18 February 2014 13:20:07 UTC