Re: Web Rule Language - WRL vs SWRL

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Bijan Parsia wrote:

>
> On Jun 22, 2005, at 2:06 PM, Jos de Bruijn wrote:
>
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>> Bijan Parsia wrote:
>
> [snip]
>
>>> That's the point, right? Queries that you might expect to return the
>>> same results on that data *don't* depending on the semantics you
>>> have for the *data*. Of course your query language might be (will
>>> be!) more expressive than your data language (see SQL).
>>
>>
>> No! As I showed in an earlier email, the ground
>
>
> Key is the slipping in of "ground".

No. For query answering only ground entailment is relevant.

>
>> entailments for both
>> semantics are *equivalent* and thus the queries would return the same
>> result.
>
>
> Of course, RDF entailment includes existential generalization, so
> that's not quite right. There seems to be more work that you need to
> do to get what you wanted (e.g., you need to look at the semantics
> of the query language; is the query "not" classical? how would that
> classical not interact with the LP semantics?)

The RDF language contains existentials and I'm not claiming that this
can be done by a rule language.
We are talking about Horn Logic and Horn Logic does not have
existentials! I never claimed this!
You claimed that a Horn formula under FOL semantics has other ground
entailments than a Horn formula under LP semantics and this is simply
not true.
I think this can conclude our discussion on this topic.

>
> Related question, what to do about BNodes? I hate them too, but they
> are there and often heavily used. They throw existentials all over
> the place, which pushes us out of plain ole datalog.

I would say: skolemize the BNodes before the rules come into play.
We will of course not achieve 100% layering, but I think this should
also not be our objective.

We have seen that the RDF semantics evolved together with the OWL
semantics such that it is now to some extent tailored to the OWL
semantics. We cannot expect this semantics to interoperate 100% with a
language developed for a different purpose.


Best, Jos

>
> Cheers,
> Bijan.
>
>
>
>


- --
Jos de Bruijn, http://www.uibk.ac.at/~c703239/
+43 512 507 6475         jos.debruijn@deri.org

DERI                      http://www.deri.org/
- ----------------------------------------------

Only two things are infinite, the universe and
human stupidity, and I'm not sure about the
former.
    -- Albert Einstein
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Received on Thursday, 23 June 2005 07:07:01 UTC