Hi Chimeze --
You wrote:
Negation as failure can be validly used to infer from a failure if the data is controlled (which is especially the case with well-designed experiments where it would be irresponsible to to do otherwise).
Agreed.
Another aspect is to use executable English descriptions of predicates [1] that depend on NAF.
Then, an answer can be of the form "Based on the data available up to 20080626...", and it can be explained in English too.
Cheers, -- Adrian
[1] Internet Business Logic
A Wiki and SOA Endpoint for Executable Open Vocabulary English over SQL and RDF
Online at www.reengineeringllc.com Shared use is free
Adrian Walker
Reengineering
On Thu, Jun 26, 2008 at 4:05 PM, Chimezie Ogbuji < ogbujic@xxxxxxx> wrote:
Just a quick comment. Pat H. wrote
[[
The basic snag with negation as failure is that it is almost always not valid. It is simply wrong. The cases where you can validly infer, from a failure to prove P, that P is false, are extremely rare. They only occur in specialized circumstances in specialized tasks performed by specialists in certain limited cases.
]]
I would disagree about this case being the exception. Negation as failure can be validly used to infer from a failure if the data is controlled (which is especially the case with well-designed experiments where it would be irresponsible to to do otherwise). If a clearly-defined protocol is used as part of the data collection process (for example, only assert P if P is known), then you can make valid inferences about missing content without the burden of classic negation, which requires a significant amount of effort (either having a large amounts of assertions about class disjointedness, etc. or requiring explicit assertions about the absence of data) to ensure that you can prove that P is false.At 8:37 PM -0400 6/25/08, Adrian Walker wrote:
Hi John --
Allow me to respond also.
You wrote...
It's important for us to develop Common Logic as the growth path
for ontologies and to incorporate CL in the Semantic MediaWiki.
Anything currently represented in either the Semantic Web notations
or relational databases can be mapped to Common Logic. And the
more compact CL notation is vastly more efficient in storage space,
transmission time, and computation time than the current Semantic
Web notations.
We should position CL as the foundation for Semantic Web 3.0.
You may like therefore to address Chris Welty's point that CL appears infeasible for the W3C rule interchange project. In slide 11 of [1], Chris says:
The CL and IKL approach [is] deprecated: infeasible for this group [W3C Rule Interchange], as major differences appeared irreconcilable (e.g. non-mon vs. mon)
He is there referring to a particular approach, viz. to adopt a highly expressive language into which all rule languages can be translated, which was used in the IKRIS project which produced IKL. If however you read on in the same slides, you will find that the language finally adopted as the initial Rule standard, though much weaker than CL, in fact is a classical logic with a classical negation, just like negation in every other logic with a clear semantics.
The fundamental difficulty seems to be
That isnt the fundamental difficulty for RIF.
that CL and IKL have chosen a theoretical semantics for negation
Its not especially 'theoretical'. It is simply what negation means in ordinary language. If you say cows are white, and I say, No, cows are brown; then my "no" says that what you said is false. That simply is what negation means. This is a common-sense, pre-theoretical notion of negation. So-called 'negation as failure' is the theoretical notion, and it only arises from database theory. The basic snag with negation as failure is that it is almost always not valid. It is simply wrong. The cases where you can validly infer, from a failure to prove P, that P is false, are extremely rare. They only occur in specialized circumstances in specialized tasks performed by specialists in certain limited cases. Can you prove that every finite abelian group can be expressed as the direct sum of cyclic subgroups of prime-power order? Answer quickly. Suppose, just for the sake of argument, that you can't. Are you justified in concluding that this is false? Maybe you had better hedge your bets.
from before the computer era, whereas SQL and most logic based programming languages use a different meaning for negation -- one that can also be formalized, e.g. as in [2].
It can be formalized, for sure. It can in fact be formalized in many different, incompatible, ways. All of them however make it vividly clear that this is not a generally correct inference rule.
Pat
Thanks for your thought about this.
-- Adrian
[2] Backchain Iteration: Towards a Practical Inference Method that is Simple
Enough to be Proved Terminating, Sound and Complete. Journal of Automated Reasoning, 11:1-22
Internet Business Logic
A Wiki and SOA Endpoint for Executable Open Vocabulary English over SQL and RDF
Online at www.reengineeringllc.com <http://www.reengineeringllc.com> Shared use is free
Adrian Walker
Reengineering
On Mon, Jun 23, 2008 at 10:54 PM, John F. Sowa <sowa@xxxxxxxxxxx> wrote:
Peter,
Thanks for posting the audio for Mark Greaves talk. I wasn't
able to log in for the talk, but I read the slides. The audio
covers some important points that are not in the slides:
http://ontolog.cim3.net/cgi-bin/wiki.pl?ConferenceCall_2008_06_19
The Semantic MediaWiki is very important work, and since it is
available as open source, we should use it.
But one important point that Mark mentioned is that the reasoning
capabilities of current Semantic Web technology is very weak.
RDF(S), OWL, SPARQL, and RuleML are useful, but weak subsets
of Common Logic.
It's important for us to develop Common Logic as the growth path
for ontologies and to incorporate CL in the Semantic MediaWiki.
Anything currently represented in either the Semantic Web notations
or relational databases can be mapped to Common Logic. And the
more compact CL notation is vastly more efficient in storage space,
transmission time, and computation time than the current Semantic
Web notations.
We should position CL as the foundation for Semantic Web 3.0.
John
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