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Re: Proposal and Test cases (Re: skolems: visible differences?)

From: Bijan Parsia <bparsia@cs.man.ac.uk>
Date: Thu, 17 Jan 2008 10:27:19 +0000
Message-Id: <D0FA726A-0924-461F-9FD2-6FCBE8F55713@cs.man.ac.uk>
Cc: "Web Ontology Language ((OWL)) Working Group WG" <public-owl-wg@w3.org>
To: "Michael Schneider" <schneid@fzi.de>

On 17 Jan 2008, at 09:15, Michael Schneider wrote:

> Jeremy Carroll wrote:
>
>> TEST 5:
>>     ObjectPropertyAssertion(:p :x _:y)
>>
>> does not entail
>>
>>     ObjectPropertyAssertion(:p :x _:y)
>
> For my understanding: Is the purpose of this testcase to show that  
> each
> occurrence of the same bNode under skolem semantics actually stands  
> for a
> fresh variable? So even an additional axiom
>
>   SameIndividuals(_:y _:y)
>
> wouldn't help, since this is not better than stating
>
>   SameIndividuals(<u> <w>)
>
> for otherwise unused URIs '<u>' and '<w>'. Is this right?
[snip]

No. Bnodes are reset at graph boundaries. In your user the two  
occurrences of the token "_:y" necessarily occur in the same context,  
thus in the same scope, thus co-refer.

There is no "official" way of demarking a graph, so, in general it's  
probably better to think of two operations, UNION and MERGE where the  
first, roughly, tries to smush bnodes where possible and the second  
tries to keep them distinct. It's a bit tricky because in the  
abstract syntax, we don't have labels at all, but most people focus  
pretty hard on the labels and how things more or less naturally work  
with labels.

I didn't work quite to the end, but the next several paragraphs seem  
based on the above misunderstanding.

Cheers,
Bijan.
Received on Thursday, 17 January 2008 10:25:38 GMT

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