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Re: finite approximation of the minimal Herbrand model for a RIF Core/BLD ruleset.

From: Jos de Bruijn <debruijn@inf.unibz.it>
Date: Wed, 24 Feb 2010 12:38:38 +0100
Message-ID: <4B850FBE.80206@inf.unibz.it>
To: Axel Polleres <axel.polleres@deri.org>
CC: Sandro Hawke <sandro@w3.org>, Birte Glimm <birte.glimm@comlab.ox.ac.uk>, SPARQL Working Group <public-rdf-dawg@w3.org>

>> On 2010-02-24 12:24, Axel Polleres wrote:
>>> Below I forward some thought from jos on this with his consent:
>>>
>>> @jos: can you ealborate what exactly you mean here:
>>>
>>>> 2- the RDF(S) semantics gives you more than just blank nodes.
>>>
>>> in how far is this a (potential) problem?
>>
>> I'm not saying this is a problem per se. You were simply not taking the
>> RDF(S) semantics (i.e., axiomatic triples & semantics conditions) into
>> account in the definition you proposed.
> 
> yes, this is another issue. good point. 
> 
>> Of course one needs to be careful with the infinite axiomatic triples,
>> especially when considering query answering and not just checking
>> entailment.
> 
> A common way to deal with this in a finite approximation way is 
> a) ignoring (specifically the infinite) axiomatic triples alltogether 
> b) take only those from the infinite axiomatic triples (those about container membership properties)
> that appear in the graph... I believe the latter is what we do in the current RDF(S) entailment regime, yes Birte?

b) seems to be the most reasonable way to go; but make sure to include
at least one representative (for queries with blank nodes).
Unnecessarily ignoring parts of the semantics (as in a) seems rather a
bad idea.


Cheers, Jos

> 
> Axel
> 
>>
>>
>> Jos
>>
>>>
>>> Axel
>>>
>>>
>>>> ============================================================================
>>>> On 2010-02-24 12:07, Axel Polleres wrote:
>>>>>
>>>>> On 24 Feb 2010, at 11:04, Jos de Bruijn wrote:
>>>>>> On 2010-02-24 11:28, Axel Polleres wrote:
>>>>>>> Hi Jos,
>>>>>>>
>>>>>>> Can you check this briefly and tell me whether I don't oversimplify
>>>>>>> things here?
>>>>>>
>>>>>> I will have a more detailed look at it later on, but a few first comments:
>>>>>> - you do not consider equality between data values, e.g.
>>>>>> "1"^^int="1"^^decimal
>>>>>
>>>>> hmmm, I am at the moment, not sure how far this is a problem, but I definitly should include this in the issues!
>>>>>
>>>>>
>>>>>> - I did not see how a minimal model for RIF-RDF combinations is defined,
>>>>>> in particular I see no blank nodes or RDF(S) semantics
>>>>>
>>>>> ? Can't we just treat them as skolem constants? We are just interested in query answering...
>>>>
>>>> 1- if you treat blank nodes as skolem constants you need to say so.
>>>> 2- the RDF(S) semantics gives you more than just blank nodes.
>>>>
>>>>> if you agree, I forward your comments to SPARQL, ok?
>>>>
>>>> Sure.
>>>>
>>>>
>>>> Jos
>>>
>>>
>>
>> --
>> Jos de Bruijn
>>   Web:   http://www.debruijn.net/
>>   Phone: +39 0471 016224
>>   Fax:   +39 0471 016009
>>
> 

-- 
Jos de Bruijn
  Web:   http://www.debruijn.net/
  Phone: +39 0471 016224
  Fax:   +39 0471 016009
Received on Wednesday, 24 February 2010 11:38:27 GMT

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