Re: SWRL expression in a property instance?

From: Benjamin Grosof (
Date: 02/12/05

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    Hi folks,
    I have a comment/question about Peter's answer.
    At 09:58 AM 2/12/2005 -0500, Peter F. Patel-Schneider wrote:
    >[Speaking for myself, but with some pretensions to know something about the
    >topic. :-) ]
    >From: David Martin <martin@AI.SRI.COM>
    >Subject: SWRL expression in a property instance?
    >Date: Fri, 11 Feb 2005 18:10:45 -0800
    > > Greetings Mike and all joint committee folks -
    > >
    > > Lest you guys get bored, a bunch of us are grappling with the question
    > > of how to use a SWRL expression as the value of a property instance, and
    > > I'd very much appreciate your views on this.
    >You asked, so don't get mad at the answer.  :-)
    > > For example, in OWL-S an AtomicProcess has a precondition, which we want
    > > to express in SWRL.  Here's a simplistic example of the kind of thing we
    > > might like to do:
    > >
    > > <AtomicProcess>
    > >    <hasPrecondition>
    > >      <ruleml:Imp>
    > >        <ruleml:body>
    > >          <!-- empty body -->
    > >        </ruleml:body>
    > >        <ruleml:head>
    > >         <swrl:IndividualPropertyAtom>
    > >           <swrl:propertyPredicate
    > >             rdf:resource="&eg;hasCreditCardOfType"/>
    > >           <swrl:argument1 rdf:resource="#user" />
    > >           <swrl:argument2 rdf:resource="#VISA" />
    > >         </swrl:IndividualPropertyAtom>
    > >        </ruleml:head>
    > >      </ruleml:Imp>
    > >    </hasPrecondition>
    > >    ....
    > > </AtomicProcess>
    > >
    > > This says that the precondition for the atomic process is that the user
    > > must have a VISA card (user is a variable that will get bound to some
    > > kind of user ID, when the process runs).
    > >
    > > So here are my questions:
    > >
    > > (1) Is this legal to use an Imp instance in this way, as the value of a
    > > property instance?
    >Your question is not specific enough.  Let me provide answers to several
    >more specific questions.
    >(11) Is the above syntactically-valid RDFS?
    >      No, because it is missing rdf:parseType="Collection" in two places.
    >(12) Ignoring that, is the above syntactically-valid RDFS?
    >      I think so.  (Checking RDF by hand is beyond my capabilities.)
    >(13) Is the above (modified) semantically-valid RDFS, i.e., non contradictory?
    >      Yes, of course, as it is very hard to make contradictions in RDFS.
    >(14) Is the above (modified) syntactically-valid OWL?
    >      Yes, although only OWL Full, as it uses collections outside of the DL
    >      syntax.
    >(15) Is the above (modified) semantically-valid OWL Full?
    >      Yes, as there is no use of interesting OWL stuff here.
    >(16) Is the above (modified) syntactically-valid SWRL.
    >      Yes, it appears to be, although the precise characteristics of the RDF
    >      syntax for SWRL are not very well specified.
    I thought in SWRL we were only permitting OWL-DL stuff not OWL-Full stuff?
    >(17) Is the above (modified) semantically-valid SWRL.
    >      Hmm.  That depends.  The RDF syntax for SWRL is not fully mixable
    >      with other RDF.  This goes to the heart of the problem with RDF.
    >      (More below on this.)
    > > (1a) In general, can SWRL classes like Imp and IndividualPropertyAtom be
    > > instantiated and used in all the same ways that ordinary OWL classes can
    > > be used in OWL-DL?  (Is it even right to think of these as OWL classes?)
    >Good question.
    >The answer to all of these is "NO!", or, at least "DON'T DO IT!".  You are,
    >in essence, mixing together facts and code without being able to determine
    >which is which.  In particular, as far as SWRL is concerned you have a
    >top-level rule there - not a precondition.  Any SWRL processor would be
    >correct in trying to determine the consequences of this rule, which is
    >certainly not what you want.
    >However, if you don't care about SWRL processing, then go right ahead.  But
    >then why worry about the RDF form of the rule - why not just include the
    >abstract syntax in a string?
    > > (2) If the above example is legit, how about if we omit the Imp and body
    > > and head elements, and just nest the IndividualPropertyAtom directly
    > > inside the hasPrecondition tag?
    >If the above considerations didn't matter, then there would be no problem.
    >Just think of it as any other data.  Again, however, why not just use
    >strings to carry the SWRL rules?
    > > (3) If the answer to (1) or (2) is "no" - is it any different for SWRL-FOL?
    >No.  There is no reason that the answer would be less restrictive for
    >SWRL-FOL.  There is no RDF syntax for SWRL FOL, nor will there ever be if I
    >have anything to say about it.
    >[In fact, it is demonstrably impossible to have a viable same-syntax
    >extension of RDF to unary/binary predicate calculus with equality.]
    > > (4) If the above example is legit, and *if* we forget about RDF
    > > semantics, will a SWRL reasoner treat the Imp as if it were a non-nested
    > > assertion, and try to reason with it?  Or will it simply record that
    > > there's an Imp instance related to an AtomicProcess instance?
    >Hmm.  A SWRL reasoner probably woudn't work very well at all on a document
    >of this form.  The RDF syntax for SWRL rules isn't really RDF - it is just
    >a way to get RDF parsers to not choke on SWRL rules.  (Why do this?  I
    >plead the fifth!)
    >If you want to write SWRL then you should have separate documents for OWL
    >information and SWRL rules.
    >If you want to embed SWRL in something else, then you should probably not
    >use the RDF syntax.
    > > Thanks!
    > >
    > > - David Martin
    > > (on behalf of various people working on OWL-S and Protege-based OWL 
    > editors)
    >Peter F. Patel-Schneider
    >Bell Labs Research
    >PS: I'm not particularly satisfied with the way this answer turned out.  In
    >particular, there are ways around your problem - but you probably won't
    >like the answer.  This topic really requires an interactive session to give
    >it full justice.
    Prof. Benjamin Grosof
    Web Technologies for E-Commerce, Business Policies, E-Contracting, Rules, 
    XML, Agents, Semantic Web Services
    MIT Sloan School of Management, Information Technology group or

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