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Re: Fw: First order logic and SPARQL

From: Sandro Hawke <sandro@w3.org>
Date: Mon, 06 Sep 2010 08:58:26 -0400
To: Julian Nolan <julian.nolan@bluewin.ch>
Cc: Semantic Web <semantic-web@w3.org>
Message-ID: <1283777906.7748.163.camel@waldron>
[including the list, to reduce the impulse for private replies.]

On Mon, 2010-09-06 at 10:19 +0200, Julian Nolan wrote:
> Hi, how can I unsubscribe from these posts?

See http://www.w3.org/Mail/Request

(It's the standard way.)

Or do you just mean how can you unsubscribe to the threads about
nonmonotonicity?   :-)   

     -- Sandro

> Thanks
> 
> Julian
> ----- 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 12:58:34 GMT

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