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Re: Issue: Add hasValue to OWL Lite

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Wed, 11 Dec 2002 22:41:32 +0000
Message-ID: <15863.48924.429616.434323@merlin.horrocks.net>
To: Jim Hendler <hendler@cs.umd.edu>
Cc: Frank van Harmelen <Frank.van.Harmelen@cs.vu.nl>, www-webont-wg@w3.org

On December 11, Jim Hendler writes:
> 
> At 11:08 PM +0100 12/10/02, Frank van Harmelen wrote:
> >Deb,
> >
> >Thanks for your summary of the discussion and lay-out of the options:
> >
> >Deborah McGuinness wrote:
> >
> >>
> >>I see the following options emerging from the discussion surrounding adding
> >>hasValue to OWL Lite.
> >>This attempts to choose highlights from the email discussion with the
> >>subject OWL Lite semantics as well.
> >>
> >>1 - do not add any notion of hasValue to OWL Lite.
> >>[...]
> >>2 - add hasValue to OWL Lite with the semantics as specified in OWL DL.
> >>[...]
> >>3 - add hasValue to OWL Lite with a restricted semantics.  A restricted
> >>semantics was proposed by Jeremy.
> >
> >I also largely follow your trade-off of the options:
> >
> >3 is not feasible at this time (on top of which I support earlier 
> >discussion this week which makes it clear that it's not even an 
> >attractive option)
> 
> I agree 3 is not feasible at this time (although I'm not sure I agree 
> with the parenthetical given Pat's responses to Ian)
> 
> >
> >2 makes OWL Light so close to OWL DL that OWL Light would loose its 
> >right to exist (remember that also Jeremy's proposal was aimed 
> >making OWL Light lighter, while this option would make it 
> >significantly heavier)
> 
> <chair hat off!>
> 
> I disagree with the above.  So far all I have seen is a bald 
> assertion by Ian that hasvalue is hard to implement.

I object most strenuously to being accused of having said something so
patently stupid as "hasvalue is hard to implement". What I said was
that *adding hasValue to OWL Lite* would make the *resulting logic* much
harder to implement.

>  As I've made 
> clear often in the WG, I don't care much about computational 
> complexity - because at web scales the issue is a red herring in my 
> opinion (nor do I see any proof that LITE is in a lower complexity 
> class without hasvalue).

But you mention below having seen pointers to the literature that
demonstrates just this. I can also refer you back to the thread
beginning with [1] for one of the many occasions when we have covered
this before! It contains a pointer into the literature and a more
intuitive explanation that I gave in response to requests from the
WG.

>  Implementationally, every major KR system I 
> know of has a hasvalue in some form, all my tools do, and I don't see 
> it as particularly hard to implement.  In fact, in several of our 
> databased-implementations (cf. Parka [1]) it is absolutely trivial to 
> implement.

All this critically depends on our definition of "implement".

> 
>   Perhaps more importantly, we've had several requests for hasvalue 
> being included in Lite in our comments list

Then *tell them to use OWL DL*. As I have already pointed out, adding
hasValue to OWL Lite makes it more or less identical to OWL DL; and if
it is really so easy to implement, then it wont be a problem, will it.

Ian

[1] http://lists.w3.org/Archives/Public/www-webont-wg/2002Jun/0094.html




- including from Protege, 
> one of the most used systems of any of those we are considering in 
> our implementation report (Protege has close to 5000 registered 
> users, and an active users mailing list with nearly 1000 members)! 
> If we decide not to include hasvalue in Lite and if we go to LC and 
> get this same comment, we will have to have a better answer than "Ian 
> asserted it was hard to implement" - and we will have to have that 
> answer formally recorded and documented per W3C process on addressing 
> Last Call comments.  We don't lightly ignore input on our WDs and I 
> sure don't see anything yet on our mailing list that a disgruntled 
> commenter couldn't appeal.
> 
> Sorry Ian, but all I've seen from you is pointers to work about 
> computational complexity -- and I just don't see that as a compelling 
> reason not to include an easy to implement, important feature that 
> our users are requesting.
> 
>   -JH
> 
> >
> >This leaves option 1 to me. Apparently, this is just the way the world is:
> >those people who will want to use has-value will end up using OWL-DL 
> >(nothing wrong with that).
> >Wanting OWL Lite to be *light* and at the same time include all the
> >most-frequently-used primitives is simply not going to work (and why 
> >should it).
> 
> I still don't see any argument that convinces me that hasvalue is any 
> worse than anything else in the language with respect to *light*ness, 
> and it is alot easier to implement in my systems than several things 
> already in Lite (for example the cardinality constraints).
> 
> <chair hat back on>
>   -JH
> 
> 
> [1] http://www.mindswap.org/2002/parka
> -- 
> 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 Wednesday, 11 December 2002 17:41:43 GMT

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