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Re: RIF+SPARQL (was Re: Entailment regimes open issues)

From: Birte Glimm <birte.glimm@comlab.ox.ac.uk>
Date: Mon, 8 Feb 2010 15:33:18 +0000
Message-ID: <492f2b0b1002080733h367b8610qe7355e5e27cfc7ec@mail.gmail.com>
To: Ivan Herman <ivan@w3.org>
Cc: Sandro Hawke <sandro@w3.org>, SPARQL Working Group <public-rdf-dawg@w3.org>
>> The general idea, I gather, is to be able to do SPARQL queries against a
>> RIF-powered deductive triple store.
>
> Correct. I do not think this requires more explanation: this is a
> succinct description of what the other entailment regime descriptions
> aim to achieve...

Now that some entailment regimes are defined, I think they give a good
example of what needs to be done and how it can be done.


>>                                     But I don't understand what needs
>> to be spec'd for that; it seems to me like the parts fit together in
>> exactly one obvious way.  (RIF certainly anticipates this use case; we
>> have a Feature At Risk on 1-to-1 lists: rdf:Lists map to RIF lists, but
>> do they map back?  I hope so, but no one has implemented that yet.)
>>
>
> And I do not expect to be complicated, just one has to have the right
> terms...

Could all be very easy, it is just hard for me to judge without first
getting more into RIF for which I unfortunately don't have much time
at the moment.

> SPARQL 1.0 had an 'extension point'[1] which means describing what it
> means when the basic graph pattern matching is extended to something
> more complex. Birte gives a nice description on what should be done
> in[2], actually. For the RIF case, one has to specify those conditions
> (even if they turn out to be obvious).
>
> In my understanding, what has to be done is to specify
>
> 1. A subset of RDF graphs called well-formed for the regime: I believe
> that can be any RDF graphs for RIF (here is where the issue with lists
> may come in if I understand the problem well)
> 2. An entailment relations between well formed graphs which, in the case
> of RIF, is probably fully defined by the RIF+RDF semantics, and a
> reference might just be fine

I tried to not mess with the already defined entailment relations. If
RIF defines an entailment relation this might be used as is.

> 3. A set of conditions that guarantee that every input yields a finite
> set of answers (modulo RDF graph equivalence)
>
> Due to blank node and such the tricky part is usually #3 and Birte has
> come up with some clean conditions on how that can be achieved with
> RDF(S) (essentially, blank nodes are skolemized before making the
> inferences, ie, only those blank nodes may appear in the answer that
> were part of the original graph pattern; I hope Birte will accept my
> characterization).
Yes that characterises it.

> As far as I could see the same approach would work
> for RIF as well, mapping these blank nodes to RIF local symbols instead
> of skolemization (or after skolemization?)
>
> Ie, I do not think it is a long editing work but certainly requires
> somebody who knows the right references and terminology and also knows
> where the possible pitfalls are...

I agree. It might all work in the same way as RDF(S), but we better
have somebody how knows whether there are additional pitfalls.
Birte

> I.
>
>
> [1] http://www.w3.org/TR/rdf-sparql-query/#sparqlBGPExtend
> [2] http://www.w3.org/TR/2010/WD-sparql11-entailment-20100126/#t13
>
>>       -- Sandro
>
> --
>
> Ivan Herman, W3C Semantic Web Activity Lead
> Home: http://www.w3.org/People/Ivan/
> mobile: +31-641044153
> PGP Key: http://www.ivan-herman.net/pgpkey.html
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> vCard  : http://www.ivan-herman.net/HermanIvan.vcf
>
>



-- 
Dr. Birte Glimm, Room 306
Computing Laboratory
Parks Road
Oxford
OX1 3QD
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+44 (0)1865 283529
Received on Monday, 8 February 2010 15:33:48 GMT

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