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Re: Issue-130 (conformance)

From: Ivan Herman <ivan@w3.org>
Date: Mon, 08 Sep 2008 20:25:04 +0200
Message-ID: <48C56E00.60501@w3.org>
To: Sandro Hawke <sandro@w3.org>
CC: Ian Horrocks <ian.horrocks@comlab.ox.ac.uk>, W3C OWL Working Group <public-owl-wg@w3.org>


Sandro Hawke wrote:
> 
> In SPARQL (which doesn't provide this information), we can do an in-band
> query for reasoner metadata like this:
> 
>    SELECT ?completeness [...your vars...]   {
>         ?g1 { [...your pattern...] } 
>         { ?g1 owlq:completenessLevel ?completeness } 
>    }
> 
> I think this works (thanks to Eric Prud'hommeaux for working it out with
> me), but it would require standardizing one RDF predicate (written here
> as owlq:completenessLevel).  It's kind of an outlier -- it's certainly
> not part of the OWL language -- but we could be defined in some normative
> appendix.

But the down side is that we, sort of, require to modify all relevant
SPARQL implementations to return this information. This also means that
one is supposed to use SPARQL in a particular way when using such a
store. I am not sure this is realistic or worth pushing...

To go back to the original issue and Ian's proposal: I actually do not
have a problem with the current formulation for entailement checkers.
Yes, implementation may simply say that they return UNKNOWN if they do
not want to go down the path of the theorem 1 checking, and that is fine
with me.

Unless we go along with the extra stuff above, I'm still not fully sure
what this whole thing means for the implementation pattern where a, say,
forward chaining engine like Oracle's expands the graph (that include
the ontology) and then SPARQL queries are issued on the result. After
all, SPARQL queries do not usually return True or False, they either
bindings to patterns or they do not return any binding. My rough reading
is that applications should interpret an empty binding return as
'unknown', and that is it; the underlying OWL-RL implementation does not
necessarily have anything else to do. (I know implementation may
implement more rules than those listed in our document, but that is
another issue.)

Is that correct? It does not feel 100% right, but I cannot put my finger
on it...

Ivan

> 
>      -- Sandro
> 

-- 

Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
PGP Key: http://www.ivan-herman.net/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf


Received on Monday, 8 September 2008 18:25:34 GMT

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