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Re: [SWC] Re: [OWL Compatibility] Re: RIF & OWL compatibility

From: Enrico Franconi <franconi@inf.unibz.it>
Date: Thu, 12 Jan 2006 11:56:38 +0100
Message-Id: <43DF3B72-EF80-4A24-A900-34185B762F61@inf.unibz.it>
Cc: public-rif-wg@w3.org
To: Jos de Bruijn <jos.debruijn@deri.org>


On 12 Jan 2006, at 11:46, Jos de Bruijn wrote:
>>> Wrt. the existential information: the semantics of LP rules is
>>> based on
>>> Herbrand models, which means (among other things) that every
>>> individual
>>> in the universe is represented with a name in the language. This  
>>> makes
>>> it impossible to truly capture existential information.
>>
>> I disagree. For example, In Rosati's approach non-distinguished
>> varibales (i.e., existentials) are not restricted to the herbrand
>> universe. BTW all the use cases in Managing Incomplete Information
>> <http://www.w3.org/2005/rules/wg/wiki/
>> Managing_incomplete_information> would be correctly handled by
>> Rosati's approach.
>
> Rosati uses the standard names assumption, which excludes considering
> unnamed individuals, thus, certain kinds of existential knowledge  
> cannot
> be captured in his approach.

As in none LP based approaches.

> If you have a name for the individual, then you can certainly deal  
> with
> it in the logic program.
> However, if we would take the following example:
>
> take the following first-order sentence:
> \exists x. p(x)
>
> and the following rule:
>
> r <- p(x)
>
> One cannot conclude r, because there is no name a such that p(a).

In Eiter, the above rule would not derive r, and in Rosati it  
couldn't even be written since it is not DL-safe. You could  
automatically make it DL-safe, and then you wouldn't derive r either.

However, unlike Eiter, and unlike pure LP based approaches, in his  
recent work Rosati does allow for several kind of classical  
existentials. For example, the use cases involving OWL-Lite in  
<http://www.w3.org/2005/rules/wg/wiki/ 
Managing_incomplete_information> would be captured correctly by  
Rosati but not by Eiter.

cheers
--e.
Received on Thursday, 12 January 2006 10:57:00 GMT

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