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Re 2: [TF-ENT] RDFS entailment regime proposal

From: Ivan Herman <ivan@w3.org>
Date: Sun, 27 Sep 2009 20:31:02 +0200
Message-ID: <4ABFAF66.107@w3.org>
To: Birte Glimm <birte.glimm@comlab.ox.ac.uk>
CC: SPARQL Working Group <public-rdf-dawg@w3.org>
Birtet,

I actually have two more technical questions. I may be very well wrong 
on two accounts, though.

1. What does it mean, in the case of RDFS, that a graph is inconsistent? 
I tried to find out how a _valid_ RDFS graph could be inconsistent... 
and I did not find it. Can you help in giving an example for what you 
were thinking about?

2. About those extra conditions that we have already discussed. The 
second one is taking care of the proliferation of blank nodes. That is 
clearly necessary and fine. However... for the 1st restriction referring 
to the subject position: isn't it only the rdf:_i properties that are 
the possible source of problems? My impression is that only those 
properties, more exactly the relevant axiomatic triples, that are 
leading to an infinite number of triples. If so, isn't it simpler to 
refer, in that first condition, to the rdf:_i properties only, ie, 
restrict the axiomatic triples only to those rdf:_i-s that are in the 
graph. It would not be different on the output side, but it may be more 
easily understandable for the everyday users. The current condition is a 
bit complex to explain to a lambda user...

(AFAIK, this is almost what Herman ter Horst does in his well known 
paper. More exactly, I think he allows for a bit more than what you 
describe: he takes the maximum 'n' for which an rdf:_n is in the Graph, 
and restricts the axiomatic triples to the rdf:_i i<=n cases. That could 
be a reasonable alternative, too, although generating some more triples 
than your restriction.)

What do I miss?

Thanks

Ivan



Birte Glimm wrote:
> Hi all,
> whoever is interested in RDFS entailment: I would be very happy about
> comments and suggestions for the RDFS entailment regime as outlined
> in:
> http://wiki.webont.org/page/SPARQL/OWL
> 
> Ignore the OWL part for now. It is not at all finished and will
> certainly change! Axel, can you check whether that would work with
> what you have in mind for RIF? My RIF knowledge is far too limited to
> judge that :-(
> 
> There are a view design choices that I have listed at the end of the
> section on RDFS, which could be an alternative to the currently
> proposed way of restricting the answers sets to a finite size. Please
> let me know prefer any of them or have any other suggestions. Ideally,
> a monotonic behavior for queries would be very nice, but that is not
> easy to achieve when solution sequences are possibly infinite without
> restrictions.
> 
> I would like to get access to the CVS and work in a real template. Who
> can arrange that?
> 
> Cheers,
> Birte
> 
> PS: Our email server is still behaving strangely regarding W3C
> messages and I do not even get my own messages, so I might get your
> answers with some delay only :-(
> 

-- 

Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153
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Received on Sunday, 27 September 2009 18:28:07 GMT

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