Michael J. Maher

FLAP Journal 2021 Journal Article

Strategic Argumentation.

• Guido Governatori
• Michael J. Maher
• Francesco Olivieri

Dialogue games are a dynamic form of argumentation, with multiple parties pooling their arguments with the intention of settling an issue. Such games can have a variety of structures, and may be collaborative or competitive, depending on the motivations of the parties. Strategic argumentation is a class of competitive dialogue games in which two players take turns in contributing their arguments, each attempting to have an issue settled in the way that they would prefer. Thus strategic argumentation games are less about discovering a joint truth than about a player imposing their view on an opponent. They are reflective of legal argumentation. In the games we study, players have perfect information of the moves players make, but incomplete information on the possible moves (arguments) that other players have available to them. We look both at games using logically structured arguments and games using abstract arguments. We show that playing these games can be computationally hard. We also examine issues of corruption in such games, and discuss approaches to foiling it.

ECAI Conference 2014 Conference Paper

Comparing Defeasible Logics

• Michael J. Maher

In this paper we seek to formally establish the similarities and differences between two formalizations of defeasible reasoning: the defeasible logics of Nute and Maier, and defeasible logics in the framework of Antoniou et al. Both families of logics have developed from earlier logics of Nute, but their development has followed different paths and they are formulated very differently. We examine these logics from the standpoint of relative inference strength - how much the logics can infer from a given theory - and relative expressiveness - how well one logic can simulate another. We identify similarities between logics in the two families and pinpoint aspects that distinguish them.

EUMAS Conference 2014 Conference Paper

Strategic Argumentation Under Grounded Semantics is NP-Complete

• Guido Governatori
• Michael J. Maher
• Francesco Olivieri
• Antonino Rotolo
• Simone Scannapieco

Abstract We study the complexity of the Strategic Argumentation Problem for 2-player dialogue games where a player should decide what move to play at each turn in order to prove (disprove) a given claim. We shall prove that this is an NP-complete problem. The result covers one the most popular argumentation semantics proposed by Dung [ 4 ]: the grounded semantics.

IJCAI Conference 2009 Conference Paper

• Michael J. Maher

Open forms of global constraints allow the addition of new variables to an argument during the execution of a constraint program. Such forms are needed for difficult constraint programming problems where problem construction and problem solving are interleaved. However, in general, filtering that is sound for a global constraint can be unsound when the constraint is open. This paper provides a simple characterization, called contractibility, of the constraints where filtering remains sound when the constraint is open. With this characterization we can easily determine whether a constraint is contractible or not. In the latter case, we can use it to derive the strongest contractible approximation to the constraint. We demonstrate how specific algorithms for some closed contractible constraints are easily adapted to open constraints.

TCS Journal 2009 Journal Article

Local consistency for extended CSPs

• Michael J. Maher

We extend the framework of Constraint Satisfaction Problems to make it more suitable for/applicable to modern constraint programming languages where both constraint satisfaction and constraint solving have a role. Some rough principles for local consistency conditions in the extended framework are developed, appropriate notions of local consistency are formulated, and relationships between the various consistency conditions are established.

LPAR Conference 2008 Conference Paper

On Computing Constraint Abduction Answers

• Michael J. Maher
• Ge Huang

Abstract We address the problem of computing and representing answers of constraint abduction problems over the Herbrand domain. This problem is of interest when performing type inference involving generalized algebraic data types. We show that simply recognizing a maximally general answer or fully maximal answer is co-NP complete. However we present an algorithm that computes the (finite) set of fully maximal answers of an abduction problem. The maximally general answers are generally infinite in number but we show how to generate a finite representation of them when only unary function symbols are present.

TIME Conference 2002 Conference Paper

Applying Local Search to Temporal Reasoning

• John Thornton 0001
• Matthew Beaumont
• Abdul Sattar 0001
• Michael J. Maher

Local search techniques have attracted considerable interest in the artificial intelligence (AI) community since the development of GSAT (Selman et al. , 1992) and the min-conflicts heuristic (Minton et al. , 1992) for solving large propositional satisfiability (SAT) problems and binary constraint satisfaction problems (CSPs) respectively. Newer SAT techniques, such as the Discrete Langrangian Method (DLM) (Shang and Wah, 1998), have significantly improved on GSAT and can also be applied to general constraint satisfaction and optimisation. However, local search has yet to be successfully employed in solving temporal constraint satisfaction problems (TCSPs). We argue that current formalisms for representing TCSPs are inappropriate for a local search approach, and we propose an alternative CSP-based end-point ordering model for temporal reasoning. In particular we look at modelling and solving problems formulated using Allen's (1983) interval algebra (IA) and propose a new constraint weighting algorithm derived from DLM. Using a set of randomly generated IA problems, we show that our local search outperforms Nebel's (1997) backtracking algorithm on larger and more difficult consistent problems.

ECAI Conference 2000 Conference Paper

A Family of Defeasible Reasoning Logics and its Implementation

• Grigoris Antoniou
• David Billington
• Guido Governatori
• Michael J. Maher
• Andrew Rock

ECAI Conference 2000 Conference Paper

An Argumentation-Theoretic Characterization of Defeasible Logic

• Guido Governatori
• Michael J. Maher

TCS Journal 1997 Journal Article

Constrained dependencies

• Michael J. Maher

We extend the notions of functional and finiteness dependencies to apply to subsets of a relation that are specified by constraints. These dependencies have many applications. We are able to characterize those constraint domains which admit a polynomial time solution of the implication problem (assuming P≠NP) and give an efficient algorithm for these cases, modulo the cost of constraint manipulation. For other cases we offer approximate algorithms. Finally, we outline some applications of these dependencies to the analysis and optimization of CLP programs and database queries.

TCS Journal 1993 Journal Article

A transformation system for deductive database modules with perfect model semantics

• Michael J. Maher

We present a transformation system for deductive database (DDB) modules. We show that it preserves several data-dependency properties of a DDB and is correct for the “perfect model” semantics of DDBs. Perfect models are not directly amenable to logical reasoning since logically equivalent DDBs may have different perfect models. We develop an approach which involves using a condition on data dependencies in DDBs (stratification compatibility) to pass from a logical equivalence to equivalence under perfect model semantics. This is readily applicable to the transformation system.

MFCS Conference 1991 Invited Paper

Elimination of Negation in Term Algebras

• Jean-Louis Lassez
• Michael J. Maher
• Kim Marriott

Abstract We give an informal review of the problem of eliminating negation in term algebras and its applications. The initial results appear to be very specialized with complex combinatorial proofs. Nevertheless they have applications and relevance to a number of important areas: unification, learning, abstract data types and rewriting systems, constraints and constructive negation in logic languages.