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Re: Web Rule Language - WRL vs SWRL

From: Bijan Parsia <bparsia@isr.umd.edu>
Date: Tue, 28 Jun 2005 18:49:45 -0400
Message-Id: <089a83c0166c5ed4376bf31398ef9781@isr.umd.edu>
Cc: www-rdf-rules@w3.org
To: Michael Kifer <kifer@cs.sunysb.edu>

[Trimming down to www-rdf-rules]
On Jun 28, 2005, at 3:09 PM, Michael Kifer wrote:

> This wasn't clear from the paper.
> In any case, the claimed interoperability doesn't extend to the more
> powerful languages.

That this wasn't claimed (or at least strongly suggested) certainly 
isn't clear from the architecture diagram that has rules and OWL 
"overlapping" with DLP. Similarly, the DLP "shield" diagram also 
strongly suggests that the interoperabilty isn't restricted in the way 
you suggest.

> 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.

Er... I do? Really? Bit odd for a black box integration approach, I 

(If my query contains an explicit default negation operator, this is 
closer, although (given non-distinguished variables) certain 
(non-ground) things may be provable on one semantics and not the other, 
so the results might still differ. Also, cardinality/counting queries 
may (or may not!) have implicit default negation, but my expectations 
(having worked with OWL for a while) will, well, be toward an open 
world. Given that OWL will have been around (and pushed) by the W3C for 
several years before a Rules wg can produce a recommendation...things 
could get confusing.


> There will be certain amount of semantic mismatch, but this most likely
> won't matter. From talking to people I get the impression that
> they build very simple ontologies using OWL. Most of them are in DLP 
> with
> some use of cardinality restrictions. However, when I press, it turns 
> out that
> people don't understand what cardinality restrictions mean in OWL. They
> think they are like cardinality constraints in databases.

I was just reminded how similar assertions based on "taking to people" 
led to the removal of qualified cardinality restrictions in OWL. That 
turned out to be a big mistake.

(All I mean is that while I have some similar experiences, I don't have 
*enough* experience (and think no one does) in building web KR to have 
a good idea what people *should* want! I know you think that Web KR is 
not a big thing or substantively different from regular KR, but I'm not 

There are aggregation and integration support arguments from both sides 
of the divide. Anyhoo.)

> People think databases but use OWL.
> Now, this is a real semantic mismatch: people mean (and want!) one 
> thing,
> but get a completely different thing.

How is this different than arguing that OWL should be largely abandoned 
(for the SemWeb, in general)? If this is the conclusion, let's bring it 

(Obviously, a decent dialectical move on your part would be to say that 
OWL won't be able to face the competition, if it's on even ground, or, 
if it could, then proponents wouldn't try to argue against adding the 
competition except perhaps from beneficent, paternalistic "don't waste 
your time" grounds. Of course, a reply would be to point out that the 
choice won't seem so clear and so there's the possibility of damaging 
all houses with no gain.)

(Er..I could go on arguing with myself, but I don't want to have to 
auto-insult ;))

Bijan Parsia.
Received on Tuesday, 28 June 2005 22:50:02 UTC

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