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Re: Sloppy inference rules

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 7 Nov 2012 19:20:44 -0600
Cc: Richard Cyganiak <richard@cyganiak.de>, Guus Schreiber <guus.schreiber@vu.nl>, RDF WG <public-rdf-wg@w3.org>
Message-Id: <BC02B24C-7CA1-444B-ADB7-3EC0DE296318@ihmc.us>
To: Ivan Herman <ivan@w3.org>

On Nov 7, 2012, at 7:02 PM, Ivan Herman wrote:

> Ah! I think you misunderstood me. I did not mean to exchange bnodes in general; I realize that this would not work.
> 
> What I meant was the following. The current rule set associates each literal with a fresh bnode; my understanding is that a new graph is created replacing each literal with this associated counterpart for the rule engine; at the end of processing these bnodes are switched back to the original literals. What I meant is that, today, we could those associations using skolems I believe instead of bnodes. 

Ah, I see. You might be right, I would have to look at the details more carefully. There still remains the awkwardness that introducing any skolem name is not logically valid, so keeping these rules logically correct would be very tricky. We would have to treat the triples with skolem names as "illegal" in the way that I am proposing to do for generalized triples, ie they get filtered out of the results before validity is declared. Not sure that much is gained, therefore. But I promise to bear the idea in mind and check it out. 
> 
> Of course, if we use the generalized triple approach for the rules then that full association business becomes unnecessary...

Quite.

Pat

> 
> Ivan
> 
> ---
> Ivan Herman
> Tel:+31 641044153
> http://www.ivan-herman.net
> 
> (Written on mobile, sorry for brevity and misspellings...)
> 
> 
> 
> On 7 Nov 2012, at 19:22, Pat Hayes <phayes@ihmc.us> wrote:
> 
>> 
>> On Nov 7, 2012, at 9:34 AM, Ivan Herman wrote:
>> 
>>> 
>>> On Nov 7, 2012, at 10:17 , Pat Hayes wrote:
>>> 
>>> 
>> .............
>>>> So, no, you can't just use skolem URIs instead of bnodes in inference rules. The resulting rules would not even be logically valid. 
>>> 
>>> Interesting. Just for my intellectual curiosity: can you clarify that?
>> 
>> Sure. Take a simple example.
>> 
>> _:x :a ex:Fish .
>> 
>> does not entail
>> 
>> skolem:newname2346 :a ex:Fish .
>> 
>> So any rules that go from a bnode-containing triple to another triple containing the same bnode can't work by going 'through' triples in which the bnode is replaced by a skolemized URI.
>> 
>> Pat
>> 
>> 
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>> 
>> 
>> 
>> 
>> 
> 
> 

------------------------------------------------------------
IHMC                                     (850)434 8903 or (650)494 3973   
40 South Alcaniz St.           (850)202 4416   office
Pensacola                            (850)202 4440   fax
FL 32502                              (850)291 0667   mobile
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Received on Thursday, 8 November 2012 01:51:49 GMT

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