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RE: [TF-ENT] A few comments on RDFS Entailment section

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Tue, 6 Oct 2009 12:59:01 +0000
To: Birte Glimm <birte.glimm@comlab.ox.ac.uk>
CC: SPARQL WG <public-rdf-dawg@w3.org>
Message-ID: <B6CF1054FDC8B845BF93A6645D19BEA3693ECF728A@GVW1118EXC.americas.hpqcorp.net>


> -----Original Message-----
> From: b.glimm@googlemail.com [mailto:b.glimm@googlemail.com] On Behalf Of
> Birte Glimm
> Sent: 6 October 2009 13:51
> To: Seaborne, Andy
> Cc: SPARQL WG
> Subject: Re: [TF-ENT] A few comments on RDFS Entailment section
> 
> see below...
> 
> 2009/10/6 Seaborne, Andy <andy.seaborne@hp.com>:
> > More general enquiry:  (this is something that came up in the last WG
> and my recollection may be partial so forgive an ignorant question):
> >
> > Suppose
> >
> >  G    is  _:x :p :z ,
> >
> >  SG   is  _:a :p _:b
> >
> >  BGP  is   ?x :p [] .
> 
> It is not clear why :z is replaced by a blank node in the scoping
> graph. 

Mistake on my part - I was trying to simplify the example after creating it.  Bad.

> The SG should be equivalent and only blank nodes are replaced
> by blank nodes with fresh names as I understand it. The problem you
> describe below of course still exists (even if I misunderstand the def
> of SG) because you could have
> _:b1 :p :z.
> _:b2 :q :y.
> and SG
> _:sg1 :p :z.
> _:sg2 :q :y.
> 
> > Does that mean there are two solutions
> >
> > ?x = _:a
> > ?x = _:b
> 
> Even for the changed G/SG that I gave, you would have ?x=_:sg1 and
> ?x=_:sg2 I think.
> 
> > Because
> >
> > P(BGP) are well-formed RDF triples that are RDFS entailed by G
> > (C1) each subject is in the set of terms used by the scoping graph
> > (C2) μ(?x) is a blank node occurring in SG.
> 
> It occured to me that this is not nice and most likely not what we
> want, but I haven't yet come round to think about a nice solution.
> 
> > What I'm not clear about is that C1 and C2 only talk about the use in SG
> so is symmetric in _:a and _:b.  I see no asymmetry to produce one
> solution over another as it's not the use in triples in SG.  Any SG with
> more than one bNode will generate alternatives, increasing with the number
> of bNodes.
> 
> Yes :-(
> 
> > Under simple entailment matching there is one because "P(BGP) is a
> subgraph of G" and not an entailment relationship, and ?x=_:x.  (DAWG did
> try for an entailment relationship but the cardinality issues were a
> problem.)
> >
> Yes, we need a similar condition for entailment regimes but not based
> on pure subgraph matching.
> 
> For now we have this as an open problem and how queries over different
> named graphs should behave (do we take entailments into account that
> depend on triples from different named graphs). I'll try and add notes
> for these two issues in the ent. regimes doc.
> 
> Just to see whether I get simple entailment right. If you have
> :s :p :o
> and query with BGP
> ?x :p :o
> you would only get ?x=:s and not ?x=_:x for some blank node _:x,
> right? I mean you have the RDF simple entailment rules se1 and se2
> (http://www.w3.org/TR/rdf-mt/#simpleRules), which could be used to add
> _:x :p :o with se2, but you do not use that, right? For simple
> entailment one just has to check sub-graphs of the queried graph.

That's my reading.  That's what the "sub-graph" brings.

	Andy

> 
> Birte
> 
> 
> 
> >        Andy
> >
> >
> 
> 
> 
> --
> Dr. Birte Glimm, Room 306
> Computing Laboratory
> Parks Road
> Oxford
> OX1 3QD
> United Kingdom
> +44 (0)1865 283529
Received on Tuesday, 6 October 2009 13:00:01 GMT

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