Sanjay Modgil

Reasoning about preferences in argumentation frameworks

The abstract nature of Dungs seminal theory of argumentation accounts for its widespread application as a general framework for various species of non-monotonic reasoning, and, more generally, reasoning in the presence of conflict. A Dung argumentation framework is instantiated by arguments and a binary conflict based attack relation, defined by some underlying logical theory. The justified arguments under different extensional semantics are then evaluated, and the claims of these arguments define the inferences of the underlying theory. To determine a unique set of justified arguments often requires a preference relation on arguments to determine the success of attacks between arguments. However, preference information is often itself defeasible, conflicting and so subject to argumentation. Hence, in this paper we extend Dungs theory to accommodate arguments that claim preferences between other arguments, thus incorporating meta-level argumentation based reasoning about preferences in the object level. We then define and study application of the full range of Dungs extensional semantics to the extended framework, and study special classes of the extended framework. The extended theory preserves the abstract nature of Dungs approach, thus aiming at a general framework for non-monotonic formalisms that accommodate defeasible reasoning about as well as with preference information. We illustrate by formalising argument based logic programming with defeasible priorities in the extended theory.

Towards an argument interchange format

The theory of argumentation is a rich, interdisciplinary area of research straddling the fields of artificial intelligence, philosophy, communication studies, linguistics and psychology. In the last few years, significant progress has been made in understanding the theoretical properties of different argumentation logics. However, one major barrier to the development and practical deployment of argumentation systems is the lack of a shared, agreed notation or ‘interchange format’ for argumentation and arguments. In this paper, we describe a draft specification for an argument interchange format (AIF) intended for representation and exchange of data between various argumentation tools and agent-based applications. It represents a consensus ‘abstract model’ established by researchers across fields of argumentation, artificial intelligence and multi-agent systems. In its current form, this specification is intended as a starting point for further discussion and elaboration by the community, rather than an attempt at a definitive, all-encompassing model. However, to demonstrate proof of concept, a use case scenario is briefly described. Moreover, three concrete realizations or ‘reifications’ of the abstract model are illustrated.

A general account of argumentation with preferences

This paper builds on the recent ASPIC^+ formalism, to develop a general framework for argumentation with preferences. We motivate a revised definition of conflict free sets of arguments, adapt ASPIC^+ to accommodate a broader range of instantiating logics, and show that under some assumptions, the resulting framework satisfies key properties and rationality postulates. We then show that the generalised framework accommodates Tarskian logic instantiations extended with preferences, and then study instantiations of the framework by classical logic approaches to argumentation. We conclude by arguing that ASPIC^+@?s modelling of defeasible inference rules further testifies to the generality of the framework, and then examine and counter recent critiques of Dung@?s framework and its extensions to accommodate preferences.

Proof Theories and Algorithms for Abstract Argumentation Frameworks

Previous chapters have focussed on abstract argumentation frameworks and properties of sets of arguments defined under various extension-based semantics. The main focus of this chapter is on more procedural, proof-theoretic and algorithmic aspects of argumentation. In particular, Chapter 2 describes properties of extensions of a Dung argumentation framework 〈A ,R〉 under various semantics. In this context a number of questions naturally arise:

The ASPIC + framework for structured argumentation: a tutorial

This article gives a tutorial introduction to the ASPIC+ framework for structured argumentation. The philosophical and conceptual underpinnings of ASPIC+ are discussed, the main definitions are illustrated with examples and several ways are discussed to instantiate the framework and to reconstruct other approaches as special cases of the framework. The ASPIC+ framework is based on two ideas: the first is that conflicts between arguments are often resolved with explicit preferences, and the second is that arguments are built with two kinds of inference rules: strict, or deductive rules, whose premises guarantee their conclusion, and defeasible rules, whose premises only create a presumption in favour of their conclusion. Accordingly, arguments can in ASPIC+ be attacked in three ways: on their uncertain premises, or on their defeasible inferences, or on the conclusions of their defeasible inferences. ASPIC+ is not a system but a framework for specifying systems. A main objective of the study of the ASPIC+ f...

Towards a Formalisation of Electronic Contracting Environments

Clauses within contracts may be thought of as norms, specifying permissions, obligations and prohibitions on contract parties. In this paper, we present a formal representation of contracts, focusing on the specification of a model of norms. With this model, a norm is associated with a status, which may change as the environment, and the status of other norms, changes. We define a normative environment, which may be used to track the status of a set of norms throughout their lifecycle, and then describe a predicates that may be used to evaluate a norms status. Agents are able to use these predicates to reason about the status of norms, and how their actions will affect the normative environment. Finally, we show the applicability of our framework to real world domains by monitoring the execution of a contract taken from a real world scenario.

Increasing Human-Organ Transplant Availability: Argumentation-Based Agent Deliberation

Human-organ transplantation is the only effective therapy for many life-threatening diseases. However, despite an increase in transplant successes, the lack of a concomitant increase in donor organ availability has led to a growing disparity between supply and demand. Much research has thus focused on defining and implementing policies for increasing donor availability, identifying suitable organ recipients, and documenting transplant procedures. A novel organ-selection process uses a multiagent system called Carrel+ to let geographically dispersed transplant physicians deliberate over organ viability to increase the availability of organs for transplantation

Metalevel argumentation

The abstract nature of Dung’s theory of argumentation accounts for its wide-spread application as a general framework for various species of non-monotonic reasoning, and, more generally, reasoning in the presence of conflict. In this article, we formalize reasoning about argumentation within the Dung argumentation paradigm itself. A metalevel Dung argumentation framework is itself instantiated by arguments that make statements about arguments, their interactions, and their evaluation in an object-level argumentation framework.We show how Dung’s theory, and object-level extensions of Dung’s theory, such as those intended to accommodate preferences, can then be uniformly characterised by metalevel argumentation in a Dung framework. We then discuss how this provides for application of the full range of theoretical and practical developments of Dung’s theory, to extensions of Dung’s theory, and provides for integration and further augmentation of these extensions.

The Added Value of Argumentation

We discuss the value of argumentation in reaching agreements, based on its capability for dealing with conflicts and uncertainty. Logic-based models of argumentation have recently emerged as a key topic within Artificial Intelligence. Key reasons for the success of these models is that they are akin to human models of reasoning and debate, and their generalisation to frameworks for modelling dialogues. They therefore have the potential for bridging between human and machine reasoning in the presence of uncertainty and conflict. We provide an overview of a number of examples that bear witness to this potential, and that illustrate the added value of argumentation. These examples amount to methods and techniques for argumentation to aid machine reasoning (e.g. in the form of machine learning and belief functions) on the one hand and methods and techniques for argumentation to aid human reasoning (e.g. for various forms of decision making and deliberation and for the Web) on the other. We also identify a number of open challenges if this potential is to be realised, and in particular the need for benchmark libraries.

An Abstract Theory of Argumentation That Accommodates Defeasible Reasoning About Preferences

Dungs abstract theory of argumentation has become established as a general framework for non-monotonic reasoning, and, more generally, reasoning in the presence of conflict. In this paper we extend Dungs theory so that an argumentation framework distinguishes between: 1) attack relations modelling different notions of conflict; 2) arguments that themselves claim preferences, and so determine defeats, between other conflicting arguments. We then define the acceptability of arguments under Dungs extensional semantics. We claim that our work provides a general unifying framework for logic based systems that facilitate defeasible reasoning about preferences. This is illustrated by formalising argument based logic programming with defeasible priorities in our framework.