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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@[65.217.30.94]>
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
>ontology.
>
>>
>>  >  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).

>Firing
>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.

Pat

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
>high."
>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.


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Received on Monday, 15 April 2002 10:57:40 GMT

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