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Fw: First order logic and SPARQL

From: Julian Nolan <julian.nolan@bluewin.ch>
Date: Mon, 6 Sep 2010 10:19:51 +0200
Message-ID: <2DB8A698A1A5440898D0E8EABAEC776F@JCNPC>
To: "Semantic Web" <semantic-web@w3.org>
Hi, how can I unsubscribe from these posts?


----- Original Message ----- 
From: "Bijan Parsia" <bparsia@cs.man.ac.uk>
To: "Pat Hayes" <phayes@ihmc.us>
Cc: "Semantic Web" <semantic-web@w3.org>; <public-sparql-dev@w3.org>
Sent: Monday, September 06, 2010 10:14 AM
Subject: Re: First order logic and SPARQL

> On 6 Sep 2010, at 02:29, Pat Hayes wrote:
> [snip]
>> This is NOT non-monotonic. The NOT EXISTS conclusion that a triple  
>> does not occur in an identified RDF graph is a perfectly monotonic  
>> inference. It becomes non-monotonic only when you go on to conclude  
>> that if said triple does not occur there, it is false.
> That can't be right. I get a non-monotonic consequence relation if I  
> conclude it is true based on its absence.
>> However, neither RDF nor SPARQL supports this further conclusion.  
>> Thus, while the SPARQL in query #13 in [1] is (of course) correct,  
>> the English gloss given to is subtly incorrect. What that query asks  
>> is not, as Lee claims, "Find me members of the Senate Armed Service  
>> committee's Strategic Forces subcommittee who do not also serve on  
>> the Personnel subcommittee.", but rather ""Find me members of the  
>> Senate Armed Service committee's Strategic Forces subcommittee who  
>> are not listed in the Personnel subcommittee RDF graph."
> But this is exactly epistemic reflection.
> The fundamental marker of non-monotonic consequence is that for some  
> KB, some assertion (A), and some consequence (C), KB |- C and (KB + A)  
> |\- C, where the plus is simple set-theoretic expansion.
> NOT EXISTS seems to meet that criterion. The set of answers shrinks as  
> we set theoretically add triples to the graph. You can preserve  
> monotonicity of the consequence relation by treating the "real" KB as  
> some sort of expanded with the consequences (e.g., filling out the  
> "blank" part of the table with explicit nulls). But then, you no  
> longer merely add A, but you also retract the null. But this just  
> shifts the non-monotonicity to insertion time.
>> (And similarly for all other uses of !bound trickery.)
> ? !bound says "Entail some answer iff the variable in the graph  
> pattern isn't bound, i.e., there is no corresponding ground entailment".
>> Now, of course, I am being pendantic, since we all know that this  
>> RDF graph is complete, so that if someone isn't listed there, then  
>> they aren't serving on the subcommittee. But *that* inference is not  
>> part of the RDF graph, is not represented by the RDF graph, s not  
>> justified by the semantics of the RDF graph, and is not used by the  
>> SPARQL machinery or justified by the SPARQL semantics.
> I don't see that. (Even before, I thought !bound introduced non- 
> monotonicity.)
>> So, Bijan's brain fart was in fact not a fart at all.
> I think it was, even if, contrary to fact, I had gotten the right  
> answer. I was overeager to refute the connection between being  
> commutative and having a formal spec. My bad.
>> The semantics of SPARQL, even with all the tricks and Bob  
>> MacGregor's complaints to the contrary,  is perfectly monotonic.
> On 6 Sep 2010, at 07:56, Pat Hayes wrote:
> [snip]
>> I guess it is in a sense, though I'd like to see the example before  
>> committing myself. My point however was directed at the assumption  
>> that implementing not-exists queries itself made the logic  
>> nonmonotonic, which is incorrect.
> The consequence relation which includes, in its consequence language  
> "NOT EXISTS", even in the form you asserted above, has to be non-mon.  
> It doesn't make the consequence relation between RDF graphs non-mon  
> (obviously), but one can lose "NOT EXISTS" answers (entailments)  
> merely by adding statements.
> Cheers,
> Bijan.
Received on Monday, 6 September 2010 11:09:54 UTC

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