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Re: Signalling entailment in queries

From: Steve Harris <steve.harris@garlik.com>
Date: Wed, 21 Jul 2010 10:04:20 +0100
Cc: SPARQL Working Group <public-rdf-dawg@w3.org>
Message-Id: <BEEF7A06-A8BE-41FF-9DCF-D6C1B6C7868E@garlik.com>
To: Sandro Hawke <sandro@w3.org>
I'm not sure I follow what this approach does.

What about the case where the service just runs all the triples through a reasoner (Pellet etc.) and then imports the output? Would everything then be regarded as ground facts? Or would you still want to distinguish between step 0. ground facts, and the inferred, but also now ground ones?

[ apologies for any naming abuse, hope that question makes sense, it's been a few years since I devoted any brainwidth to inference ]

- Steve
On 2010-07-20, at 19:22, Sandro Hawke wrote:

> In discussing the graph naming issue and the related service description
> issue today, I agreed to take my concern/proposal to e-mail
> [ACTION-282].
> The basic problem I have is this: I think people will be very confused
> if SPARQL end points start to quietly do inference.  This confusion will
> result in software doing the wrong thing, with possibly serious results.
> Some of the blame will, rightly, land on "SPARQL inference".
> Alternatively, for fear of this, public end points will just not do
> inference.
> What we've got so far is the idea that folks should look at the service
> description.   I think this is probably too "quiet".  As Souri pointed
> out today, what happens if you looked at the service description at 5pm
> and inference gets turned on at 6pm?  Yes, we can probably find
> workarounds -- like saying you should use a different end point address
> any time you make this kind of change to the SD -- but I'm thinking it's
> better to just add something to the query language.    Listening to
> folks in the meeting talk about it, I thought of this:
>        SELECT * FROM NAMED <g1> 
>        WHERE { GRAPH <g1> ENTAILS { ?x rdfs:subClassOf ?y } }
> Here, the system making the query is explicitly asking for inference, so
> no harm can be done by the end-point suddenly turning on inference, as
> long as it still allows querying of the pre-inference graph.  If the
> end-point doesn't want to keep the pre-inference graph around, then
> users will have to modify their queries to include the ENTAILS
> keyword, ... but that seems right, since those users will need to think
> about whether the change in results is okay for their application.
> In this design, the kind of entailment would be specified in the SD. 
> It's tempting to also allow parameterization of the entailment regime,
> perhaps like this:
>    PREFIX ent <http://www.w3.org/ns/entailment/>
>        SELECT * FROM NAMED <g1> 
>        WHERE { GRAPH <g1> ENTAILS BY ent:RDFS { ?x
>        rdfs:subClassOf ?y } }
> I understand this parameterization is similar to the out-of-scope
> "Parameterized Inference" feature [1], but perhaps if it's really as
> simple as this, it's okay to do anyway.   (If not, is there a way to
> suggest that everyone implement it the same way, even if it's not in the
> spec?  :-)
> Finally, I wanted to thank folks for reminding me of the incorrectness
> of thinking of the entailments of a graph as another graph.  Under
> entailment regime E, graph G will entail graphs G0, G1, ... Gn, rather
> than a single graph GE.  In many simple cases, the merge of G0...Gn is
> also entailed and can be used as the single graph-of-all-entailments,
> but in cases with disjunction, such a union is not itself entailed, so
> there is no graph-of-all-entailments.  (I've learned and forgotten this
> too many times, sorry.)
> One more thought -- I'm not sure the word "entails" is the best word
> here.  Perhaps "IMPLIES" would make more sense to relevant audience. 
>    -- Sandro
> [1] http://www.w3.org/2009/sparql/wiki/Feature:ParameterizedInference

Steve Harris, CTO, Garlik Limited
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Received on Wednesday, 21 July 2010 09:04:58 UTC

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