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Studies on Disjunctive Logic Programming

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Chiaki Sakama

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Kyoto University, 1994.
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## Abstract

Recent studies have enriched the expressive power of logic programming as
a knowledge representation tool and the growing importance of logic programming in
artificial intelligence is well recognized these days.
Disjunctive logic programming is one of such extensions of logic programming
which provides us with the ability of reasoning with indefinite information.
Due to their expressiveness, disjunctive logic programming has been given an
increasing attention over the past few years.
In this dissertation, we study theoretical frameworks for disjunctive logic
programming. Our particular interest is in the semantic issues of
disjunctive logic programs and their correspondences to commonsense reasoning
in artificial intelligence.
As a semantics of disjunctive logic programs, we propose a new
declarative semantics called the possible model semantics.
The possible model semantics is an alternative theoretical framework for
disjunctive logic programs, which provides a flexible inference
mechanism for representing knowledge and also has a computational
advantage over the classical minimal model semantics.
To relate disjunctive logic programs to commonsense reasoning in
artificial intelligence, we propose transformations from disjunctive
logic programs to various forms of nonmonotonic reasoning such as default
logic, circumscription, and autoepistemic logic.
Moreover, we discuss connections
between disjunctive logic programs and abductive logic programs,
and reveal close relationships between each framework.
Another important issue for commonsense reasoning is the treatment of
inconsistent knowledge.
Since classical logic programming is not useful in inconsistent programs,
we introduce paraconsistent semantics for disjunctive logic programs
which provide uniform frameworks for handling both
indefinite and inconsistent information in a program.
We finally discuss program optimization issues in disjunctive logic programs.
A technique of partial deduction in logic programming is extended
to disjunctive logic programs and its correctness is presented.

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