W3C home > Mailing lists > Public > www-rdf-rules@w3.org > December 2003

Local Closed World Paper

From: Adrian Walker <adrianw@snet.net>
Date: Wed, 03 Dec 2003 14:52:40 -0500
Message-Id: <5.0.2.1.2.20031203143920.02323c50@pop.snet.net>
To: Drew McDermott <drew.mcdermott@yale.edu>, <phayes@ai.uwf.edu>
Cc: www-rdf-rules@w3.org, www-rdf-interest@w3.org, www-rdf-logic@w3.org, heflin@cse.lehigh.edu

Drew, Pat --

I have been following your debate about NAF (below) with great interest.

There's a paper  "LCW-Based Agent Planning for the Semantic Web"  by
Jeff Heflin and Hector Muņoz-Avila  that addresses how to get the best of 
both worlds.

You can download it from http://www.cse.lehigh.edu/~heflin/

Hope this helps,

                                     Cheers,  --  Adrian



                                            INTERNET BUSINESS LOGIC

                                              www.reengineeringllc.com

Dr. Adrian Walker
Reengineering LLC
PO Box 1412
Bristol
CT 06011-1412 USA

Phone: USA 860 583 9677
Cell:    USA  860 830 2085
Fax:    USA  860 314 1029


At 02:00 PM 12/3/03 -0500, you wrote:


>    [me]
>    >The NAF approach is likely to be much more efficient, much easier to
>    >implement, and much more likely to yield a useful conclusion than the
>    >heavy-duty theorem prover.
>
>    [Pat Hayes]
>    All true. It is also likely to be wrong,
>    unfortunately. The fact that you can't think of a
>    closer airport doesn't usually qualify as a good
>    reason to conclude that there isn't one, unless
>    you also know for sure that you know all the
>    airport locations, so that if you don't know it,
>    then its not there. Like, for example, if you
>    have a  list of all the airports. If you make
>    this explicit, as you should, then you are back
>    doing 'heavy-duty' reasoning.
>
>I was trying to stay within the vocabulary of the example, and I was
>assuming a plausible context that I didn't state, namely that someone
>was planning a trip.  If you replace "nearest airport" by "nearest
>airport reasonable to travel someplace from here," then negation as
>failure is a reasonable strategy, assuming you know all the airports
>in the vicinity.
>
>    BTW, calling it 'heavy-duty' is misleading. In
>    the first case you have made all the equality
>    reasoning explicit. In a prolog-style
>    implementation this is all buried in the
>    backtracking done by the interpreter: but it
>    still needs to be done. The same actual
>    *reasoning* is involved in both cases.
>
>Yes.  But the NAF version is stylized in a way that permits efficient
>implementation.  If you could be sure that the alternative always
>involved iterating through a list and doing a set of equality
>substitutions, you could probably find an equally efficient
>implementation.  (I've often wondered why no one has worked on this.)
>In the general case, though, you have to have a system that does
>general-purpose reasoning about equality, which can involve a lot of
>search.
>
>    >  I hope the people who deprecate it realize
>    >that the heavy-duty theorem prover is the only alternative.
>
>    Its not a matter of alternatives. If you want to
>    draw checkable valid conclusions, then you need
>    to do this kind of reasoning.
>
>I don't want to draw checkable valid conclusions.
>
>    If you want to
>    make random guesses and hope for the best then
>    you can of course work faster, but don't expect
>    others to believe in your conclusions.
>
>At least I'll _have_ conclusions.
>
>    Negation-as-failure is NOT a good general
>    reasoning strategy: 99.99% of the time it will
>    immediately produce childishly ludicrous
>    conclusions: I don't know anyone called Jose, so
>    there isn't anyone called Jose; I never heard of
>    SARS, ...
>
>Where have you been?
>
>Of course negation-as-failure is not the way to handle "not" in
>general; it's the way to handle it when you don't care about possible
>nearby secret airports and the like.
>
>    The
>    industrial uses of Prolog-style rules all are
>    designed within controlled environments,
>    typically using databases, where such special
>    conditions can be assumed.
>
>To repeat what I said above, if you use NAF as an efficient way to
>draw valid conclusions, you're right.  I prefer to think of it as a
>way to draw conclusions that may well be wrong, in situations where
>the wrongness of a probably correct conclusion is not fatal.  The
>burden is on someone who finds this distasteful to show that pure
>deductive techniques will suffice for real-world applications.
>
>                                              -- Drew
>
>--
>                                              -- Drew McDermott
>                                                 Yale University CS Dept.
Received on Wednesday, 3 December 2003 14:48:06 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 December 2009 10:53:11 GMT