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Re: Web Rule Language - WRL vs SWRL

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Wed, 29 Jun 2005 23:16:26 +0100
Message-Id: <6f2c9a5deea50c37c38d40d27c5c9d45@cs.man.ac.uk>
Cc: Bijan Parsia <bparsia@isr.umd.edu>, Jim Hendler <hendler@cs.umd.edu>, www-rdf-rules@w3.org, dreer@fh-furtwangen.de, Jos de Bruijn <jos.debruijn@deri.org>
To: Michael Kifer <kifer@cs.sunysb.edu>

On 29 Jun 2005, at 22:37, Michael Kifer wrote:


>>>>> N3 is essentially a different syntax for F-logic and its extensions
>>>>> (but
>>>>> N3's semantics is defined by use cases ;-). As far as I can tell,
>>>>> with
>>>>> each
>>>>> new presentation that I hear N3 is moving in the direction of LP.
>>>> I think that we should stick to discussing how things actually *are*
>>>> rather than directions in which you hope/believe they might be 
>>>> moving.
>>> I am discussing things as they already are. N3 now has a form of 
>>> SNAF.
>> Maybe, but this doesn't make it LP - we have long since known how to
>> support a form of SNAF in DL using the so-called K operator.
> What makes something an LP language?

You tell me - you are the one who is claiming that things are "moving 
in the direction of LP".

>> N3 is also
>> based on RDF, and RDF does not make a CWA and so if fundamentally
>> incompatible with LP (as you seemed to agree in an answer to an 
>> earlier
>> email - see below).
> Disagree.
>>>> Surely N3 is *actually* a different syntax for RDF, plus some
>>>> rule-like
>>>> extensions. As we have already agreed, LP is semantically 
>>>> incompatible
>>>> with RDF, so it does not make sense to say that N3 can be included 
>>>> in
>>>> LP.
>>> Did we agree about RDF?  I didn't notice that.
>> To quote from one of your earlier emails:
>>> Your argument is well-taken. However, if you are querying an ontology
>>> with
>>> an LP language then you expect that CWA will be applied in the 
>>> current
>>> state.
>>> That is, if your DLP ontology says that John has one child, Bill, and
>>> nothing else, then your query "get all people who have exactly one
>>> child"
>>> (a query like the one in your paper) is expected to return John, 
>>> since
>>> in
>>> the current state he is not known to have more children.
>> So, an LP language would find an entailment that is *not* supported by
>> RDF semantics (which would allow for models in which John had other
>> children). Ergo, LP is semantically incompatible with RDF.
> You misunderstood my reply.
> I meant that I acknowledged your point about more expressive languages
> not giving the same answers when they are both applied to the same 
> dataset.
> RDF by itself doesn't have any queries defined over it, so it is
> meaningless to claim that a query language L over RDF syntax is
> incompatible with RDF.

This is not what is being claimed. What is being claimed is that an RDF 
triple of the form <x,P,y> is *not* semantically equivalent to the LP 
rule P(x,y). This is the equivalence that is implicit in the layering 
that we have been discussing (i.e., LP on top of DLP on top of RDF), 
and which leads to LP entailments that are not valid w.r.t. the 
semantics of RDF (or DLP).


> 	--michael
Received on Wednesday, 29 June 2005 22:16:43 UTC

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