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Re: OWL Lite vs OWL DL-Lite

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Mon, 17 Feb 2003 18:49:14 +0000
Message-ID: <15953.11946.894318.462627@galahad.cs.man.ac.uk>
To: Jim Hendler <hendler@cs.umd.edu>
Cc: Evan Wallace <ewallace@cme.nist.gov>, www-webont-wg@w3.org

On February 16, Jim Hendler writes:
> 
> At 23:01 +0000 2/16/03, Ian Horrocks wrote:
> >On February 13, Evan Wallace writes:
> >>
> >>
> >>  Deb McGuinness wrote regarding OWL F Lite and OWL DL Lite
> >>
> >>  >I think ian's examples are valid real world examples of usefulness
> >>  >of OWL Lite DL.
> >>  >
> >>  >Essentially they are characterized by an application being able to
> >>  >take advantage of a reasoner's ability to classify descriptions
> >>  >correctly.  this requires iff semantics.
> >>  >
> >>  >Similarly I think there are users who come more from a modeling
> >>  >orientation who would like a simple transition path up from rdfs
> >>  >and would benefit from an OWL lite that does not require them to
> >>  >understand the limitations imposed by DL.
> >>
> >>  Speaking as someone who comes from the world of modeling (which I
> >>  take to mean data modeling and object modeling), I don't see this
> >>  at all.  People who are currently modeling using NIAM/ORM, EXPRESS,
> >>  or UML who are considering using Semantic Web languages will go
> >>  directly to OWL DL Lite or OWL DL (or perhaps to DAML).  At OMG,
> >>  we are specifically asking for a mapping to OWL DL in our RFP for
> >>  Ontology Definition (an OMG version of a UML Presentation syntax
> >>  for OWL).  This is because the motivation for moving models to
> >>  ontology languages is to attain a practical capability for reasoning
> >>  about those models.  I am not denying that there is a constituency
> >>  for a migration path from RDFS to OWL F Lite, just that I haven't
> >>  encountered it in OMG, ISO STEP, or other communities doing
> >>  manufacturing, business, or systems modeling. 
> >
> >Good to hear you say that. This has also been my experience in the
> >bio, medical and e-science communities.
> >
> >>
> >>  Speaking for Two Dimensions in Lite
> >>
> >>  One public relations issue that I have encountered regarding OWL is
> >>  the perception that it is not worth looking into the language because
> >>  it contains a union of the problems, limitations, and disliked features
> >>  of RDF(S) and DLs (many of which are actually mis-perceptions, outdated
> >>  understandings, and/or prejudice).  This suggests to me a good reason
> >>  for adopting a two dimensional structure for the OWL sublanguages.  It
> >>  would show clearly that there is a partial decoupling in the language
> >>  between RDF and Description Logics that allows users to pick the
> >>  sublanguage with the features they need, rather than being limited to
> >>  one design compromise in merging the two.
> >
> >The trouble with this is that it is VERY hard to see the justification
> >for the existence of OWL F Lite - it is in no sense Lite, and the loss
> >of a couple of constructors w.r.t. OWL full is of trivial significance
> >compared to the semantic and computational complexities you get by
> >mixing RDF with a standard logic.
> >
> >Ian
> 
> [probably chair hat off so as not to offend anyone by my having an opinion]
> 
> Very Hard??? We heard several implementors get up at the f2f and say 
> they would like to do Full semantics limited to the Lite vocabulary, 
> and we've seen similar on our public comments list and in the 
> feedback we've gotten from RDF Core people -- so maybe as Pat has 
> said there are two different communities here.  For what it is worth, 
> not only do I find it not hard at all to see the justification but, 
> in fact, the data seems to agree -- that is, many of the things using 
> DAML or OWL right now are tools which add some Lite constructs to 
> RDF-Schemas, thus "enhancing" the schema with more of our 
> expressivity.

None of what you just said seems to me to be a justification for
having OWL Flite. What it does suggest is that some people may want to
use OWL full, but would be happy with (very) incomplete
implementations.

>  And, btw, the implementation simplicity argument 
> (which you are on record as saying is the only one that matters) 
> still holds - it is much easier to implement the Lite constructs than 
> the whole kit and kaboodle.

In what sense is it easier? I presume you don't know of a decision
procedure or even if one is possible. If we therefore assume we are
talking about incomplete reasoners, then an OWL Flite reasoner would
be an OWL full reasoner, so it wouldn't be any easier to build one!

So, from a users point of view, they should be perfectly content just
to use (part of) OWL full, and from an implementors point of view, why
would they want to claim that they had implemented an OWL Flite
reasoner when they could, with zero additional effort, claim to have
implemented an OWL full reasoner?

Similarly for editing tools etc. OWL full and OWL Flite documents
would be completely interchangeable - the difference is only in the
semantic interpretations placed on some of the RDF syntax. So, an OWL
Flite tool might as well claim to be an OWL full tool.

>   In fact, however, we need not really argue, because we have already 
> created Owl Flite (it is simply using the vocabulary for Lite, as 
> defined in the Overview, without the extra cosntraints of DL).  Thus, 
> we are only talking about doing something expository.
>   We can do it now, or wait until we get asked to do it in the 
> requests from our LC -- it is an "editorial" change, not a technical 
> one, so I'm not too worried about it

The question is whether we want to have the added confusion of
additional officially labelled languages in a non-linear family
relationship. It is hard to see why we should do this in order to
introduce a new language that is to all intents and purposes
indistinguishable from OWL full.

Ian


>   -JH
> 
> 
> >  >
> >>  -Evan
> >>
> >>  Evan K. Wallace
> >>  Manufacturing Systems Integration Division
> >>  NIST
> >>  ewallace@nist.gov
> >>
> 
> 
> -- 
> Professor James Hendler				  hendler@cs.umd.edu
> Director, Semantic Web and Agent Technologies	  301-405-2696
> Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
> Univ of Maryland, College Park, MD 20742	  240-731-3822 (Cell)
> http://www.cs.umd.edu/users/hendler
> 
Received on Monday, 17 February 2003 13:48:11 GMT

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