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Re: OWL Lite semantics

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Mon, 9 Dec 2002 15:39:21 +0000
Message-ID: <15860.47401.852521.984620@merlin.horrocks.net>
To: Jim Hendler <hendler@cs.umd.edu>
Cc: "Jeremy Carroll" <jjc@hplb.hpl.hp.com>, <www-webont-wg@w3.org>

On December 9, Jim Hendler writes:
> (This message follows those by Peter, Pat and Ian)
> 
> The formalists heard from, here's my "scruffy" response
> 

[snip]

> SEMANTICS:
> 
> Pat and Ian claim Jeremy's proposal is somehow significantly 
> different semantically than the current one.  This confuses me - what 
> Jeremy proposes is still a proper subset of OWL DL, so I'm not sure 
> why this one is so different from our current as to make trouble - 
> can one of you explain?

I had hoped that this was exactly what I did explain in my email. To
reiterate, OWL DL is a *syntactic* subset of OWL full, but for
ontologies that fall within the OWL DL syntactic subset, the semantics
of OWL DL are equivalent to those of OWL full. So, if I ask an OWL DL
system if one OWL DL ontology entails another, it will answer yes (no)
iff an OWL full system would answer yes (no) to the same question.

Jeremy's proposal is that OWL Lite be both a syntactic and *semantic*
"subset" (I use the expression loosely in this case) of OWL DL. So,
fully compliant OWL Lite and OWL DL (and OWL full) systems could give
different answers to such entailment questions. We would therefore
have the situation where two agents could disagree as to the meaning
of some piece of OWL, both stating as their authority fully compliant
OWL reasoners. I was under the impression that the avoidance of such
situations was one of the main reasons for our emphasis on precise
semantics.

Ian



> 
> -------------------
> * - sorry, this book predates the web and I can't find the code on the web.
> [1] http://www.aaai.org/Press/Reports/Workshops/ws-99-13.html
> [2] http://www.mindswap.org/downloads.shtml
> [3] http://lists.w3.org/Archives/Public/www-webont-wg/2002Dec/0038.html
> -- 
> 
> 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<!doctype html public "-//W3C//DTD W3 HTML//EN">
> <html><head><style type="text/css"><!--
> blockquote, dl, ul, ol, li { padding-top: 0 ; padding-bottom: 0 }
>  --></style><title>Re: OWL Lite semantics</title></head><body>
> <div>(This message follows those by Peter, Pat and Ian)</div>
> <div><br></div>
> <div>The formalists heard from, here's my &quot;scruffy&quot;
> response</div>
> <div><br></div>
> <div><br></div>
> <div>EASE of implementation:</div>
> <div><br></div>
> <div>What Jeremy suggests is quite appealing to me because there is
> good evidence that it IS easier to implement -- in fact, the code foe
> a program with a considerable subset of Jeremy's OWL Lite proposal can
> be found in the 1987 AI textbook &quot;AI Programming&quot; by
> Charniak, Riesbeck, McDermott and Meehan *.</div>
> <div><br></div>
> <div>Current implementations:</div>
> <div><br></div>
> <div>In fact, a great many implemented AI systems use essentially what
> Jeremy proposes -- these are the systems that gre primarily from the
> frame systems (remember that discussion from very early in our
> group??)&nbsp; - examples of a number of these tools can be found in
> the 1999 &quot;Ontology Management Workshop&quot; that AAAI ran
> [1].</div>
> <div><br></div>
> <div>In these systems, the prevailing use has NOT been classification,
> and I'd argue that most of the &quot;only if&quot;s grow out of the
> need for classifiers (this is a simplification, I admit, but would
> take much more bandwdith to be specific).&nbsp; However, in many cases
> people build the ontology separately from classification (thus not
> needing most of the class reasoning in OWL).</div>
> <div><br></div>
> <div>For example, in all the tools built by my current group [2], we
> assume that either we are importing an ontology from elsewhere, or
> that someone is extending one by adding classes and properties to
> existing places in an ontology.&nbsp; In these cases, we are able to
> support many of the &quot;if&quot; entailments but not the only-ifs
> (c.f. my mexican restaurant example summarized by Deb in [3])</div>
> <div><br></div>
> <div>In short, under Jeremy's subset many current systems will already
> be able to handle OWL Lite, under our current definition they can't.&nbsp;
> (btw, everyone of the systems that I know of include HAS-VALUE, but
> only with the &quot;if&quot; semantics)</div>
> <div><br></div>
> <div>SEMANTICS:</div>
> <div><br></div>
> <div>Pat and Ian claim Jeremy's proposal is somehow significantly
> different semantically than the current one.&nbsp; This confuses me -
> what Jeremy proposes is still a proper subset of OWL DL, so I'm not
> sure why this one is so different from our current as to make trouble
> - can one of you explain?</div>
> <div><br></div>
> <div>-------------------</div>
> <div>* - sorry, this book predates the web and I can't find the code
> on the web.</div>
> <div>[1]<font face="Helvetica" size="+2" color="#000000">
> http://www.aaai.org/Press/Reports/Workshops/ws-99-13.html</font></div>
> <div>[2] http://www.mindswap.org/downloads.shtml</div>
> <div>[3]
> http://lists.w3.org/Archives/Public/www-webont-wg/2002Dec/0038.html</div
> >
> <x-sigsep><pre>-- 
> </pre></x-sigsep>
> <div><br></div>
> <div>Professor James Hendler<x-tab>
> </x-tab><x-tab>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
> </x-tab><x-tab>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
> </x-tab><x-tab>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </x-tab>&nbsp;
> hendler@cs.umd.edu</div>
> <div>Director, Semantic Web and Agent Technologies<x-tab>&nbsp;&nbsp;
> </x-tab>&nbsp; 301-405-2696<br>
> Maryland Information and Network Dynamics Lab.<x-tab>&nbsp;&nbsp;&nbsp;
> </x-tab>&nbsp; 301-405-6707 (Fax)<br>
> Univ of Maryland, College Park, MD 20742<x-tab>&nbsp;&nbsp;&nbsp;
> </x-tab>&nbsp; 240-731-3822 (Cell)<br>
> http://www.cs.umd.edu/users/hendler</div>
> </body>
> </html>
Received on Monday, 9 December 2002 09:39:14 GMT

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