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Re: exchanging OWL through RIF

From: Ed Barkmeyer <edbark@nist.gov>
Date: Thu, 02 Mar 2006 16:33:01 -0500
Message-ID: <4407648D.4000103@nist.gov>
To: Michael Kifer <kifer@cs.sunysb.edu>
CC: RIF WG <public-rif-wg@w3.org>

Michael Kifer wrote:

> I am having a second thought about the requirement that OWL should be
> exchangeable through RIF by encoding it in FOL (which I am guilty of voting
> for also and now attribute it to sleep deprivation :-).
> 
> I think this requirement is completely misguided.

I think the above statement of the requirement can be misunderstood, but I 
don't think the intent is at all misguided.

It is not a matter of "exchanging an OWL ontology"; the requirement is to 
deliver the semantic content of an OWL ontology as a ruleset, so that a rules 
engine can incorporate that content into its rulebase.

A pseudo use-case: A given site "Uhu" using OWL ontologies and an OWL engine 
may find it necessary to communicate with a site "Rex" that has only 
"rulesets" and "rule engines" for some task in which Uhu needs the support of 
Rex.  In this case, it is important that Uhu be able to convert the relevant 
OWL ontology to a "rules" (RIF) form, so that it can be used by Rex in 
performing its supporting task.  And the requirement for RIF is that its "FOL 
subset" be able to capture the semantics of the OWL ontology.

The alternative view of this scenario is that Uhu simply sends the OWL 
ontology, and it is incumbent on Rex to convert the OWL ontology to its 
internal "rules" form.  There is nothing wrong with this view, except that it 
has no role for RIF -- it makes the OWL->rules conversion a software project 
for the Rex engine, and another project for the ILOG engine, and another for 
the Jena engine, etc., creating lots of work for the engine providers and many 
third parties who are familiar with the proprietary rules forms.  By 
comparison, any tool that can convert OWL to RIF without loss (standard form 
to standard form) gives Uhu what is need to work with Rex, and also Rudi and 
Regina, no matter what rules engines they have.

> For interoperability, we will need to be able to send queries to OWL
> engines. Representation of those queries will need to be hashed out later.

This is, of course, exactly the inverse use case.  Here the Rex site needs the 
assistance of the Uhu site in making some inference.  But Rex does not need 
RIF for this at all, only something like SPARQL.  But suppose that Rex needs 
to send this ruleset to Regina, so that Regina can use its local KB to assist 
Rex in making some inferences.  Then when Rex sends the RIF ruleset to Regina, 
the SPARQL queries to Uhu that appear in some of the antecedents must have a 
RIF representation.  (And I think this is in some sense the degenerate case. 
It is entirely possible that Regina is a 'hybrid' site, combining both DL and 
Rules reasoning capabilities, with the consequence that Regina wants to 
"understand" the SPARQL query, not just blindly send it to Uhu.)

It seems to me that "Web-based Rules exchange" demands that we support BOTH of 
these two use cases, not just the latter.

-Ed

-- 
Edward J. Barkmeyer                        Email: edbark@nist.gov
National Institute of Standards & Technology
Manufacturing Systems Integration Division
100 Bureau Drive, Stop 8263                Tel: +1 301-975-3528
Gaithersburg, MD 20899-8263                FAX: +1 301-975-4482

"The opinions expressed above do not reflect consensus of NIST,
  and have not been reviewed by any Government authority."
Received on Thursday, 2 March 2006 21:33:11 GMT

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