Sorry, but you are missing the point. (01)
The point is that a given conclusion *can* be proven with the facts at our
disposal, it's just that we delegated the task of checking the facts to a
stupid/careless person, and they told as that they weren't able to draw the
conclusion. (02)
Please let's not muddy the waters with this discussion of NAF -- it is really a
red herring. (03)
Ian (04)
On 2 Aug 2010, at 18:54, Rich Cooper wrote: (05)
> Hi Ian,
>
> If the intent of the tool's designers is to mimic human perspectives on
> knowledge and logic, then negation as failure is more human like, IMHO, than
> any existing alternative. A person with no experience in an area normally
> is very skeptical of assertions that can't be proven within his/her database
> of factual and structural knowledge, and reaches the same conclusion. I'm
> sure you've heard it said that you don't know what you don't know, so you
> assume you know everything until proven otherwise.
>
> Another way to look at it is that, within the bounds of evidence, a judge or
> juror has no basis for any conclusion that is not consistent with known,
> demonstrated facts. It is always possible that other information will
> surface in the future, but the rational deduction of the present moment has
> to be based on known facts, not on missing information.
>
> One consequence of this result is that it is very hard to convince anyone of
> a fact which has no familiarity, in specific or general terms, to them
> personally. That is why attorneys and laws depend on known facts.
>
> -Rich
>
> Sincerely,
> Rich Cooper
> EnglishLogicKernel.com
> Rich AT EnglishLogicKernel DOT com
> 9 4 9 \ 5 2 5 - 5 7 1 2
>
> -----Original Message-----
> From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx
> [mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Ian Horrocks
> Sent: Monday, August 02, 2010 10:14 AM
> To: edbark@xxxxxxxx; [ontolog-forum]
> Cc: Bernardo Cuenca Grau
> Subject: Re: [ontolog-forum] owl2 and cycL/cycML
>
> It is even more tricky that this. The failure in "negation as failure"
> doesn't mean failure of a given algorithm, it means not provably true. There
> are many decidable logics with NAF. If we have an incomplete reasoner for
> such a logic, we are *still* incorrect if we take failure to return "True"
> as being equivalent to "False", because the failure may simply be a symptom
> of the incompleteness and nothing to do with NAF.
>
> Simple example: I am using a logic in which negation is interpreted as NAF.
> I have a simple boolean theory in which negation isn't used and which
> entails A(x). I ask if A(x) is entailed. My incomplete (for entailment)
> reasoner answers "False". If I treat this as entailing that A(x) is not
> entailed, then I am really incorrect -- nothing to do with NAF.
>
> In fact I think that we would be well advised to strike NAF from the record
> -- it's really not helpful in this discussion :-)
>
> Ian
>
>
>
>
>
> On 2 Aug 2010, at 17:45, Ed Barkmeyer wrote:
>
>>
>> Ian Horrocks wrote:
>>
>>> Regarding my claim that reasoners are typically used in a way that is
> actually incorrect, to the best of my knowledge none of the incomplete
> reasoners in widespread use in the ontology world even distinguish "false"
> from "don't know" -- whatever question you ask, they will return an answer.
> Thus, in order to be correct, applications would have to treat *every*
> "false" answer as "don't know". I don't know of any application that does
> that.
>>>
>>
>> Put another way, it is not incorrect to treat "don't know" as "false",
>> if "negation as failure" is a stated principle of the reasoning
>> algorithm. We can state the 'negation as failure' principle generally
>> as "if the assertion cannot be proved from the knowledge base, the
>> assertion is taken to be false."
>>
>> Of course, "proved" means that the reasoning algorithm can derive a
>> proof, which depends on the algorithm actually implemented in the
>> engine. As Ian mentioned earlier, this kind of "proof" implies that the
>> nature of the reasoning algorithm is, or incorporates, "model
>> construction", which is typical of various kinds of logic programming
>> engines, but there are many hybrid algorithms.
>>
>> -Ed
>>
>> --
>> Edward J. Barkmeyer Email: edbark@xxxxxxxx
>> National Institute of Standards & Technology
>> Manufacturing Systems Integration Division
>> 100 Bureau Drive, Stop 8263 Tel: +1 301-975-3528
>> Gaithersburg, MD 20899-8263 FAX: +1 301-975-4694
>>
>> "The opinions expressed above do not reflect consensus of NIST,
>> and have not been reviewed by any Government authority."
>>
>>
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