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Re: Krivov's question: "Why RDF?"

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Fri, 12 Mar 2004 21:55:02 +0000
Message-ID: <16466.12726.733824.508658@merlin.horrocks.net>
To: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Cc: Sandro Hawke <sandro@w3.org>, www-webont-wg@w3.org

On March 11, Jeremy Carroll writes:
> 
> 
> If you regard OWL as just an ontology language then basing it on RDF (at 
> all) is hard to argue for.
> But as a web ontology language perceived as layering on top of RDF 
> semantically it is plausible that the amount of effort needed to make it 
> just more triples (rather than a true syntactic extension) was worth it.
> 
> I think it comes down to the W in OWL ...
> 
> Having decided that we working on Web ontology, we had to accept a number 
> of limitations from other Web languages, RDF being one of them.

The W in OWL stands for Web. Some may argue that Web does not imply
RDF.

Ian

> 
> Jeremy
> 
> 
> 
> 
> Sandro Hawke wrote:
> 
> > re: http://lists.w3.org/Archives/Public/public-webont-comments/2004Mar/0020
> > 
> > I provoked some discussion of this matter on the the DAML/EU Joint
> > Committee list recently.  (The question there being whether or how to
> > layer a rule language (eg SWRL) on RDF.)
> > 
> >    Peter F. Patel-Schneider:
> >       I argued long and loud in the W3C WebOnt working group about
> >       problems that using the RDF syntax caused.  This argument didn't go
> >       anywhere, so I gave in and created a partial solution for OWL.  
> > 
> >    Sandro Hawke: 
> >       Do you remember why the WG disagreed with you?
> > 
> >    Peter F. Patel-Schneider:
> >       Because all Semantic Web langauges have to be same-syntax
> >       extensions of RDF. 
> > 
> >    Frank van Harmelen: 
> >       Yes, I must support this. The *only* argument for many WebOnt
> >       members to accept/put up with the RDF syntax for OWL was
> >       political pressure (perceived or real) from W3C.
> > 
> >          -- http://www.daml.org/listarchive/joint-committee/1639.html
> > 
> > I wasn't in the WG for those discussion, and I suspect the history
> > isn't as important as the future.   For people developing a rule
> > language these are important issues for the future; for this working
> > group there may be some important explanations or lessons that
> > can be offered, perhaps in response to Prof. Krivov's question.
> > 
> > Here's a strawman answer:
> > 
> >    > I completely do not understand why RDF is necessary as an
> >    > intermediate layer between XML and OWL.
> > 
> >    The short answer is that it's not theoretically necessary, but
> >    after weighing the options and issues, the working group decided
> >    that OWL would be most useful for the web community if constructed
> >    in this way.  The abstract syntax for OWL, or the XML syntax you
> >    mention, would certainly work for expressing OWL ontologies, but in
> >    the end they would not support the evolution of the Semantic Web
> >    quite as well.
> > 
> >    The arguments against they layering are fairly well known, but in
> >    terms of theoretical challenges and in terms of parsing, as
> >    explored in "Parsing OWL in RDF/XML" [1].
> > 
> >    On the other hand:
> > 
> >       (1) Relying on RDF poses no additional burden, because the
> >       properties and classes offered by an OWL ontology are offered
> >       largely for use in RDF instance data.  This means that
> >       programmers, software systems, and users working with OWL can be
> >       expected to be already comfortable with RDF and convinced of its
> >       value.  OWL users are likely to see RDF as a natural part of
> >       their system (and visa versa), while XML itself may be
> >       irrelevant to them.  (This does not justify the OWL syntactic
> >       layering, but it does help explain why the presence of RDF isn't
> >       as expensive as it might first seem.)
> > 
> >       (2) RDF users may want to use small bits of OWL that fit
> >       naturally into their RDF.  Their entire "ontology" may consist
> >       of an owl:sameAs triple, or one owl:InverseFunctionalProperty
> >       statement.  Why should they have to switch to another language,
> >       when these simple bits (like all of RDFS) fit elegantly into
> >       RDF?  If they go on to define Restrictions and other complex
> >       forms, there is no sudden jump to a new language, just a gradual
> >       use of more difficult concepts and constructs.
> > 
> >       (3) RDF systems are expected to become very sophisticated in
> >       merging data from web data sources, with caching, provenance
> >       tracking, publish/subscribe features, trust reasoning, etc.
> >       If OWL ontologies are just more RDF data, they can more easily
> >       provide these services for the OWL data needed in reasoning
> >       about the RDF data.
> > 
> >    There may be more arguments, of course.  It's not clear whether
> >    these are the arguments that swayed the working group when it first
> >    approached this question.  The group was largely following along a
> >    path which included RDFS, DAML-ONT, and DAML+OIL, and it may also
> >    have been influenced by the vision of RDF as the data-bus of
> >    semantic web [1], but one need not subscribe to these notions to be
> >    convinced.
> > 
> >    The bottomw line is that we expect certain practical advantages to
> >    result from this layering approach, and we think they outweigh the
> >    difficulties in parsing OWL from RDF/XML.  We expect that in due
> >    course these difficulties will be well understood and few people
> >    will have to deal with them directly.
> > 
> >    [1] http://www.w3.org/2000/Talks/1206-xml2k-tbl/slide10-0.html
> > 
> > Or something like that.  :-)
> > 
> >     -- sandro
> > 
> > 
> 
Received on Friday, 12 March 2004 16:59:57 GMT

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