Argument exchange over the semantic web

The Semantic Web purports to give computeraccessible meaning to the content of the World Wide Web. The rationale behind this project is to create an environment where all this information could be freely exchanged among diverse entities, yet retaining its intended meaning. Defeasible Logic Programming is a knowledge representation and reasoning formalism that by combining Logic Programming with Defeasible Argumentation is able to represent incomplete and potentially contradictory information. In this article we explore what is required in order to provide Defeasible Logic Programming knowledge representation and reasoning over the semantic web.Eje: Agentes y Sistemas InteligentesRed de Universidades con Carreras en Informática (RedUNCI

Defeasible Logic Programming: An Argumentative Approach

The work reported here introduces Defeasible Logic Programming (DeLP), a formalism that combines results of Logic Programming and Defeasible Argumentation. DeLP provides the possibility of representing information in the form of weak rules in a declarative manner, and a defeasible argumentation inference mechanism for warranting the entailed conclusions. In DeLP an argumentation formalism will be used for deciding between contradictory goals. Queries will be supported by arguments that could be defeated by other arguments. A query q will succeed when there is an argument A for q that is warranted, ie, the argument A that supports q is found undefeated by a warrant procedure that implements a dialectical analysis. The defeasible argumentation basis of DeLP allows to build applications that deal with incomplete and contradictory information in dynamic domains. Thus, the resulting approach is suitable for representing agent's knowledge and for providing an argumentation based reasoning mechanism to agents.Comment: 43 pages, to appear in the journal "Theory and Practice of Logic Programming

Handling Defeasibilities in Action Domains

Representing defeasibility is an important issue in common sense reasoning. In reasoning about action and change, this issue becomes more difficult because domain and action related defeasible information may conflict with general inertia rules. Furthermore, different types of defeasible information may also interfere with each other during the reasoning. In this paper, we develop a prioritized logic programming approach to handle defeasibilities in reasoning about action. In particular, we propose three action languages {\cal AT}^{0}, {\cal AT}^{1} and {\cal AT}^{2} which handle three types of defeasibilities in action domains named defeasible constraints, defeasible observations and actions with defeasible and abnormal effects respectively. Each language with a higher superscript can be viewed as an extension of the language with a lower superscript. These action languages inherit the simple syntax of {\cal A} language but their semantics is developed in terms of transition systems where transition functions are defined based on prioritized logic programs. By illustrating various examples, we show that our approach eventually provides a powerful mechanism to handle various defeasibilities in temporal prediction and postdiction. We also investigate semantic properties of these three action languages and characterize classes of action domains that present more desirable solutions in reasoning about action within the underlying action languages.Comment: 49 pages, 1 figure, to be appeared in journal Theory and Practice Logic Programmin

About the use of time on argumentative systems

There are many areas in Computer Science where time plays an important role. Artificial Intelligence is one of them. In this particular area Defeasible Logic Programming (DeLP) was developed to cope with incomplete and potentially inconsistent information. This formalism combines results from Logic Programming and Defeasible Argumentation. DeLP in particular provides the possibility of representing defeasible information in a declarative way and a defeasible argumentation inference mechanism to warrant conclusions. Although this formalism and Defeasible logic programming in general are very useful has left apart an issue that is crucial on several kind of problems, namely time. There are also many developments that face temporal reasoning, in particular Event Calculus, but non of them consider defeasible information or what to do if we have incomplete or not completely reliable information. In this work we try to attempt an exploration of a possible combination of these two reasoning areas, temporal and defeasible.Eje: VI Workshop de Agentes y Sistemas Inteligentes (WASI)Red de Universidades con Carreras en Informática (RedUNCI

Argumentation Semantics for Defeasible Logics

Defeasible logic is a simple but efficient rule-based non-monotonic logic. It has powerful implementations and shows promise to be applied in the areas of legal reasoning and the modelling of business rules. So far defeasible logic has been defined only proof-theoretically. Argumentation-based semantics have become popular in the area of logic programming. In this paper we give an argumentation-based semantics for defeasible logic. Recently it has been shown that a family of approaches can be built around defeasible logic, in which different intuitions can be followed. In this paper we present an argumentation-based semantics for an ambiguity propagating logic, too. Further defeasible logics can be characterised in a similar way

Defeasible Systems in Legal Reasoning: A Comparative Assessment

Different formalisms for defeasible reasoning have been used to represent legal knowledge and to reason with it. In this work, we provide an overview of the following logic-based approaches to defeasible reasoning: Defeasible Logic, Answer Set Programming, ABA+, ASPIC+, and DeLP. We compare features of these approaches from three perspectives: the logical model (knowledge representation), the method (computational mechanisms), and the technology (available software). On this basis, we identify and apply criteria for assessing their suitability for legal applications. We discuss the different approaches through a legal running example

Representation results for defeasible logic

The importance of transformations and normal forms in logic programming, and generally in computer science, is well documented. This paper investigates transformations and normal forms in the context of Defeasible Logic, a simple but efficient formalism for nonmonotonic reasoning based on rules and priorities. The transformations described in this paper have two main benefits: on one hand they can be used as a theoretical tool that leads to a deeper understanding of the formalism, and on the other hand they have been used in the development of an efficient implementation of defeasible logic.Comment: 30 pages, 1 figur

Defeasible disjunctive datalog

Datalog is a declarative logic programming language that uses classical logical reasoning as its basic form of reasoning. Defeasible reasoning is a form of non-classical reasoning that is able to deal with exceptions to general assertions in a formal manner. The KLM approach to defeasible reasoning is an axiomatic approach based on the concept of plausible inference. Since Datalog uses classical reasoning, it is currently not able to handle defeasible implications and exceptions. We aim to extend the expressivity of Datalog by incorporating KLM-style defeasi- ble reasoning into classical Datalog. We present a systematic approach to extending the KLM properties and a well-known form of defeasible entailment: Rational Closure. We conclude by exploring Datalog exten- sions of less conservative forms of defeasible entailment: Relevant and Lexicographic Closure