I just wanted to add some comments that I forgot to make in my
previous note in this thread. Following is what I did say: (01)
There are also many cases where a metalevel reasoner can
make orders of magnitude *improvement* in performance
at the object level. Among them are various kinds of
compilers that reorganize or specialize the axioms at the
object level before proceeding with the proof. (02)
Two important points to add are the following: (03)
1. Most commercially successful methods for handling defaults,
exceptions, negation-as-failure, belief revision, and
related methods of nonmonotonic reasoning already depend
on a metalevel reasoner. (04)
2. Unfortunately, that reasoner is located in the head of some
programmer, knowledge engineer, or database administrator
who is forced to anticipate all possible options and write
special-purpose code or axioms to handle them. (05)
I also cited the work by Andersen et al. as a valuable metalevel
approach for compiling from a very general, very expressive
version of logic (CycL) to a more specialized logic used in
conjunction with a relational database: (06)
Peterson, Brian J., William A. Andersen, & Joshua Engel (1998)
"Knowledge bus: generating application-focused databases from
large ontologies," Proc. 5th KRDB Workshop, Seattle, WA.
http://sunsite.informatik.rwth-aachen.de/Publications/CEUR-WS/Vol-10/ (07)
The authors used Cyc as a powerful tool for knowledge acquisition
and testing. After they had used Cyc to develop their ontology,
they used their compiler to translate the Cyc axioms to simpler
statements (Horn-clause logic and database constraints). The
result ran much faster than the original Cyc version, and it
did not require the Cyc system at run time. (08)
Unfortunately, Doug Lenat, the director of the Cyc project, lost
a fantastic opportunity. Instead of promoting Cyc as a powerful
development tool for databases and knowledge bases that could run
independently of Cyc, Doug took a very negative, defensive position.
He wanted everybody to use Cyc, and he did not want people to
compile Cyc axioms to systems that did not run the Cyc software. (09)
But by insisting on that narrow use of Cyc, Lenat lost a chance
to move Cyc into the mainstream of commercial development and
eventually the Semantic Web. (010)
I believe that commercial success of semantic technology depends
critically on moving metalevel compilers out of the heads of
professional knowledge engineers. We cannot expect large numbers
of people to learn and use RDF(S) + OWL + RuleML + SPARQL or any
similar notations. But we can expect domain experts to work with
automated and semiautomated knowledge compilers that can generate
the appropriate run-time code. (011)
John Sowa (012)
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