W3C home > Mailing lists > Public > www-webont-wg@w3.org > April 2002

Re: SEM: semantics for current proposal (why R disjoint V?) (fwd)

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Sun, 7 Apr 2002 13:17:44 -0400
Message-Id: <p0510150ab8d62de6c252@[]>
To: Ian Horrocks <horrocks@cs.man.ac.uk>
Cc: www-webont-wg@w3.org
>------- start of forwarded message -------
>From: Ian Horrocks <horrocks@cs.man.ac.uk>
>To: Dan Connolly <connolly@w3.org>
>Date: Fri, 5 Apr 2002 18:33:48 +0100
>Subject: Re: SEM: semantics for current proposal (why R disjoint V?)
>Reply-To: Ian Horrocks <horrocks@cs.man.ac.uk>
>On April 5, Dan Connolly writes:
>>  On Fri, 2002-04-05 at 07:08, Ian Horrocks wrote:
>>  > On March 21, Dan Connolly writes:
>>  > > On Thu, 2002-03-21 at 14:28, Ian Horrocks wrote:
>>  > > > On March 21, Libby Miller writes:
>>  > > > > >
>>  > > > > > As noted in the design discussions for DAML+OIL, I don't
>>  > > > > > see sufficient justification for making V disjoint
>>  > > > > > from R.
>>  > > > > >
>>  > > > > > It seems silly not to be able to talk about the intersection
>>  > > > > > of two sets of strings, or UniqueProperty's whose
>>  > > > > > range is dates, or whatever.
>>  > > >
>>  > > > This means that any OWL reasoner has to take on responsibility for
>>  > > > reasoning about types
>>  > >
>>  > > I gather when you say "OWL reasoner" you mean a complete
>>  > > reasoner.
>>  > >
>>  > > I'm not very interested in such a thing.
>>  > >
>>  > > Regular old horn-clause/datalog reasoners
>>  > > (with some built-in predicates like
>>  > > string:lessThan and such) seem
>>  > > to get me what I need pretty well.
>>  >
>>  > Dan,
>>  >
>>  > It seems that, on the basis of a few toy examples where using ad-hoc
>>  > reasoning seems give the results you want/expect, you conclude that
>>  > this will be appropriate/adequate for all applications.
>>  No, just for an interesting class of applications.
>>  By the way, if you consider
>>  formalizing the operations of W3C[1]
>>  to be a toy example, I'm interested to know what
>>  sort of applications you would take seriously.
>I didn't intend to be pejorative - I was only referring to the examples
>I have seen in email. It wasn't completely clear to me from [1] where
>the ontology comes in or what kind of reasoning is being performed,
>but I am guessing that you are not using a very large or complex
>>  >  I don't find
>>  > this argument very convincing.
>>  As I say, I didn't make that argument.
>>  I'm arguing that we can advance the state of the art
>>  without a completeness requirement.
>>  > Even w.r.t. ontology level reasoning I expect things to rapidly get
>>  > large and complex enough that humans wont be able to check all
>>  > inferences - we will just have to trust that the reasoner got it
>>  > right. Soundness is therefore essential, and completeness highly
>>  > desirable.
>>  Yes, soundness is essential.
>>  I don't see why completeness is all that interesting
>>  in the general case. I expect various reasoners
>>  to be complete for various classes of problems.
>This is one of the problems with incompleteness - it is notoriously
>difficult to characterise "classes of problem" for which such a
>reasoner is complete. See [1] for a discussion of this issue.
>>  > For example, when multiple processes are interacting, some
>>  > action may be taken by one process on the basis of a non-inference by
>>  > another process,
>>  That's non-monotonic reasoning. Part of life in the semantic
>>  web is: don't do that (without explicit license).
>I don't see that this is non-monotonic. I'm not even talking about
>changing any facts. I'm talking about the problems that can arise when
>a "negation" is inserted by a process that uses the result of a query
>to another process.

If that query was not made with an explicit reference to a closed 
world assumption as part of the query, then the assumption of the 
truth of the negation from the failure of the query is a nonmonotonic 
inference step.

>E.g., a missile defense system might be programmed
>to fire at any incoming aircraft not identified as a friendly.

Good example of a nonmonotonic inference which illustrates its 
dangers. There is a recent true-life example, by the way, involving 
an unexpected default assumption (see end of this message).

>at a friendly aircraft due incompleteness in the identification
>process might reasonably be considered as unsound behaviour on the
>part of the overall system.
>>  > so incompleteness can easily lead to "unsoundness".
>>  Unsoundness can result from all sorts of bugs; this
>>  is just one of them.
>>  Actually, unsound/heuristic reasoning can be pretty interesting,
>  > as long as it's not confused with formal reasoning; e.g.
>>	I conclude based on your recent buying patterns
>>	that the following products are likely to be
>>	interesting to you: X, Y, Z.
>>	I didn't arrive at this conclusion based on
>>	sound reasoning, so take the recommendations
>>	with a grain of salt.
>>  or
>>	I conclude, based on a search of my extensive
>>	holdings, that there are no court cases
>>	in that jurisdiction involving chimpanzees and volkswagens.
>>	Digitally signed,
>>	The BigLaw online service.
>This might be true, but I fail to see the relevance. The question I am
>addressing is, should we design the language in such a way that it is
>possible to build sound and complete reasoners for usin in
>applications where this is an important issue.

No, thats not the question, because that is trivial: there have been 
sound and complete reasoners for full first-order logic available for 
the last 30-odd years. Some of them are even quite efficient, these 
days, on almost all inputs.


PS. the example mentioned is described here:
Washington Post  March 24, 2002 Pg. 21

>'Friendly Fire' Deaths Traced To Dead Battery
Taliban Targeted, but U.S. Forces Killed

>By Vernon Loeb, Washington Post Staff Writer

>The deadliest "friendly fire" incident of the war in Afghanistan was
>triggered in December by the simple act of a U.S. Special Forces air
>controller changing the battery on a Global Positioning System device he was
>using to target a Taliban outpost north of Kandahar, a senior defense
>official said yesterday.
>Three Special Forces soldiers were killed and 20 were injured when a
>2,000-pound, satellite-guided bomb landed, not on the Taliban outpost, but
>on a battalion command post occupied by American forces and a group of
>Afghan allies, including Hamid Karzai, now the interim prime minister.
>The U.S. Central Command, which runs the Afghan war, has never explained how
>the coordinates got mixed up or who was responsible for relaying the U.S.
>position to a B-52 bomber, which fired a Joint Direct Attack Munition (JDAM)
>at the Americans.
>But the senior defense official explained yesterday that the Air Force
>combat controller was using a Precision Lightweight GPS Receiver, known to
>soldiers as a "plugger," to calculate the Taliban's coordinates for a B-52
>attack. The controller did not realize that after he changed the device's
>battery, the machine was programmed to automatically come back on displaying
>coordinates for its own location, the official said. Minutes before 
>the fatal B-52 strike, which also killed five Afghan
>opposition soldiers and injured 18 others, the controller had used the GPS
>receiver to calculate the latitude and longitude of the Taliban position in
>minutes and seconds for an airstrike by a Navy F/A-18, the official said.
>Then, with the B-52 approaching the target, the air controller did a second
>calculation in "degree decimals" required by the bomber crew. The controller
>had performed the calculation and recorded the position, the official said,
>when the receiver battery died.
>Without realizing the machine was programmed to come back on showing the
>coordinates of its own location, the controller mistakenly called in the
>American position to the B-52. The JDAM landed with devastating precision.
>The official said he did not know how the Air Force would treat the incident
>and whether disciplinary action would be taken. But the official, a combat
>veteran, said he considered the incident "an understandable mistake under
>the stress of operations."
>"I don't think they've made any judgments yet, but the way I would react to
>something like that -- it is not a flagrant error, a violation of a
>procedure," the official said. "Stuff like that, truth be known, happens to
>all of us every day -- it's just that the stakes in battle are so enormously
>Nonetheless, the official said the incident shows that the Air Force and
>Army have a serious training problem that needs to be corrected. "We need to
>know how our equipment works; when the battery is changed, it defaults to
>his own location," the official said. "We've got to make sure our people
>understand this."

That last is a wonderful example of bad system thinking, by the way.

IHMC					(850)434 8903   home
40 South Alcaniz St.			(850)202 4416   office
Pensacola,  FL 32501			(850)202 4440   fax
Received on Monday, 15 April 2002 10:57:40 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 6 January 2015 21:56:43 UTC