Norman Y. Foo

AIJ Journal 2006 Journal Article

Solving logic program conflict through strong and weak forgettings

• Yan Zhang
• Norman Y. Foo

We consider how to forget a set of atoms in a logic program. Intuitively, when a set of atoms is forgotten from a logic program, all atoms in the set should be eliminated from this program in some way, and other atoms related to them in the program might also be affected. We define notions of strong and weak forgettings in logic programs to capture such intuition, reveal their close connections to the notion of forgetting in classical propositional theories, and provide a precise semantic characterization for them. Based on these notions, we then develop a general framework for conflict solving in logic programs. We investigate various semantic properties and features in relation to strong and weak forgettings and conflict solving in the proposed framework. We argue that many important conflict solving problems can be represented within this framework. In particular, we show that all major logic program update approaches can be transformed into our framework, under which each approach becomes a specific conflict solving case with certain constraints. We also study essential computational properties of strong and weak forgettings and conflict solving in the framework.

ECAI Conference 2004 Conference Paper

Simplicity in Solving the Frame Problem

• Victor Jauregui
• Maurice Pagnucco
• Norman Y. Foo

LPAR Conference 2003 Conference Paper

A Syntax-Based Approach to Reasoning about Actions and Events

• Bao Quoc Vo
• Abhaya C. Nayak
• Norman Y. Foo

In this paper, we introduce an alternative approach to reasoning about action. The approach provides a solution to the frame and the ramification problem in a uniform manner. The approach involves keeping a (syntax-based) model of the world that is updated when actions are performed. The approach is similar to the STRIPS system in which formulas are deleted and added as effects of an action. The approach however does not suffer from STRIPS’ limitations in expressivity.

JELIA Conference 2002 Conference Paper

Interpolation Properties of Action Logic: Lazy-Formalization to the Frame Problem

• Dongmo Zhang
• Norman Y. Foo

Abstract This paper makes a contribution to the meta-theory of reasoning about action. We present two interpolation properties of action logic. We show that the frame axioms which are required for answering a query involve only the objects which are relevant to the query and action description. Moreover, if the action description is expressed by normal form, the required frame axioms depend on only the query itself. Therefore the frame problem may be mitigated by localizing descriptions and postponing the listing of frame axioms till a query occurs. This offers a pragmatic solution to the frame problem. This solution does not rest on any meta-hypotheses most existing solutions to the frame problem rely on.

IJCAI Conference 1999 Conference Paper

Diagrammatic Proofs

• Norman Y. Foo
• Maurice Pagnucco
• Abhaya C. Nayak

Diagrammatic reasoning comprises phenomena that range from the so-called "free-rides" (e. g. almost immediate understanding of visually perceived relationships) to conventions about tokens. Such reasoning must involve cognitive processes that are highly perceptual in content. In the domain of mathematical proofs where diagrams have had a long history, we have an opportunity to investigate in detail and in a controlled setting the various perceptual devices and cognitive processes that facilitate diagrammatically based arguments. This paper continues recent work by examining two kinds of diagrammatic proofs, called Categories 1 and 3 by Jamnik, et. al. 97], the first being one in which generalization of a diagram instance is implied, and the second being one in which an infinite completion is represented by an ellipsis. We provide explanations of why these proofs work, a semantics for ellipses, and conjectures about the underlying cognitive processes that seem to resonate with such proofs.

IJCAI Conference 1999 Conference Paper

Preferential Semantics for Causal Systems

• Pavlos Peppas
• Maurice Pagnucco
• Mikhail Prokopenko
• Norman Y. Foo
• Abhaya Nayak

In the present work we examine the causal theory of actions put forward by McCain and Turner [Mc- Cain and Turner, 1995] for determining ramifications. Our principal aim is to provide a characterisation of this causal theory of actions in terms of a Shoham-like preferential semantics [Shoham, 19881. This would have a twofold advantage: it would place McCain and Turner's theory in perspective, allowing a comparison with other logics of action; and, it would allow us to glean further insights into the nature of causality underlying their work. We begin by showing that our aim is not attainable by a preferential mechanism alone. At this point we do not abandon preferential semantics altogether but augment it in order to arrive at the desired result. We draw f he following moral which is at the heart of our paper: two components — minimal change under a preferential structure and causality — are required to provide a concise solution to the frame and ramification problems.

ECAI Conference 1998 Conference Paper

Updating Logic Programs

• Yan Zhang 0003
• Norman Y. Foo

TARK Conference 1996 Conference Paper

Changing Conditional Belief Unconditionally

• Abhaya C. Nayak
• Norman Y. Foo
• Maurice Pagnucco
• Abdul Sattar 0001

Although the AGM account of beliefchange tells us how to change unconditional beliefs, it fails to guide us in changing our conditional beliefs. That explains why, in the AGM account of belief change proper, a decent account of iterated belief change is not forthcoming. Darwiche and Pearl provide an account of changing conditional beliefs. We argue that the Darwiche-Pearl postulates are, on the one hand, limited in scope and, on the other, excessively strong and suggest how they should be supplemented. We show, contrary to the generally held view, that the revision operation changes to a new (though in some cases the same) revision operation after each instance of belief change. Finally, we prove what may be viewed as representation results connecting the acount offered in this paper with entrenchment kinematics.

ECAI Conference 1996 Conference Paper

Definitional Constraints

• Norman Y. Foo
• Abhaya C. Nayak
• Maurice Pagnucco

ECAI Conference 1996 Conference Paper

Learning From Conditionals: Judy Benjamin's Other Problems

• Abhaya C. Nayak
• Maurice Pagnucco
• Norman Y. Foo
• Pavlos Peppas

ECAI Conference 1996 Conference Paper

Revision vs. Update: Taking a Closer Look

• Pavlos Peppas
• Abhaya C. Nayak
• Maurice Pagnucco
• Norman Y. Foo
• Rex Bing Hung Kwok
• Mikhail Prokopenko

IJCAI Conference 1993 Conference Paper

Reasoning About Persistence: A Theory of Actions

• Yan Zhang
• Norman Y. Foo

Winslett proposed a method for reasoning about action called the possible models approach (PMA). The PMA successfully removed the major difficulty manifested by Ginsberg and Smith's possible worlds approach (PWA). In this paper, we show that Winslett's PMA fails to solve the frame and ramification problems for some actions, as does the PWA. From this observation, we classify actions as definite and indefinite, and find that, in general, the PMA is not appropriate for both definite and indefinite actions. We propose a new approach to formalize actions based on persistence. We compare our approach with the PMA in detail, and show that our new formalization can avoid the problems in the PMA and PWA in most cases, and give more intuitive results for reasoning about action, regardless of whether the action is definite or indefinite.

ECAI Conference 1990 Conference Paper

Nonmonotonic Dynamics of Default Logic

• Mary-Anne Williams
• Norman Y. Foo

IJCAI Conference 1989 Conference Paper

Minimal Change and Maximal Coherence: A Basis for Belief Revision and Reasoning about Actions

• An
• S. Rao
• Norman Y. Foo

The study of belief revision and reasoning about actions have been two of the most active areas of research in AI. Both these areas involve reasoning about change. However very little work has been done in analyzing the principles common to both these areas. This paper presents a formal characterization of belief revision, based on the principles of minimal change and maximal coherence. This formal theory is then used to reason about actions. The resulting theory provides an elegant solution to the conceptual frame and ramification problems. It also facilitates reasoning in dynamic situations where the world changes during the execution of an action. The principles of minimal change and maximal coherence seem to unify belief revision and reasoning about actions and may form a fundamental core for reasoning about other dynamic processes that involve change.