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45
An Abstract, ArgumentationTheoretic Approach to Default Reasoning
, 1997
"... We present an abstract framework for default reasoning, which includes Theorist, default logic, logic programming, autoepistemic logic, nonmonotonic modal logics, and certain instances of circumscription as special cases. The framework can be understood as a generalisation of Theorist. The generali ..."
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Cited by 162 (23 self)
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We present an abstract framework for default reasoning, which includes Theorist, default logic, logic programming, autoepistemic logic, nonmonotonic modal logics, and certain instances of circumscription as special cases. The framework can be understood as a generalisation of Theorist. The generalisation allows any theory formulated in a monotonic logic to be extended by a defeasible set of assumptions. An assumption can be defeated (or "attacked") if its "contrary" can be proved, possibly with the aid of other conflicting assumptions. We show that, given such a framework, the standard semantics of most logics for default reasoning can be understood as sanctioning a set of assumptions, as an extension of a given theory, if and only if the set of assumptions is conflictfree (in the sense that it does not attack itself) and it attacks every assumption not in the set. We propose a more liberal, argumentationtheoretic semantics, based upon the notion of admissible extension in logic pro...
Defeasible Logic Programming: An Argumentative Approach. Theory and Practice
 of Logic Programming
, 2004
"... 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 infe ..."
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Cited by 141 (37 self)
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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, i. e. 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. 1
Representation Results for Defeasible Logic
 ACM Transactions on Computational Logic
, 2001
"... 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 to ..."
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Cited by 134 (95 self)
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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
Abstract Argumentation
 ARTIFICIAL INTELLIGENCE AND LAW
, 1996
"... In this paper we explore the thesis that the role of argumentation in practical reasoning in general and legal reasoning in particular is to justify the use of defeasible rules to derive a conclusion in preference to the use of other defeasible rules to derive a conflicting conclusion. The defeasib ..."
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Cited by 85 (24 self)
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In this paper we explore the thesis that the role of argumentation in practical reasoning in general and legal reasoning in particular is to justify the use of defeasible rules to derive a conclusion in preference to the use of other defeasible rules to derive a conflicting conclusion. The defeasibility of rules is expressed by means of nonprovability claims as additional conditions of the rules. We outline an abstract approach to defeasible reasoning and argumentation which includes many existing formalisms, including default logic, extended logic programming, nonmonotonic modal logic and autoepistemic logic, as special cases. We show, in particular, that the “admissibility ” semantics for all these formalisms has a natural argumentationtheoretic interpretation and proof procedure, which seem to correspond well with informal argumentation. In the admissibility semantics there is only one way for one argument to attack another, namely by undermining one of its nonprovability claims. In this paper, we show how other kinds of attack between arguments, specifically how rebuttal and priority attacks, can be reduced to the undermining of nonprovability claims.
Propositional Defeasible Logic has Linear Complexity
 of Logic Programming
, 2001
"... Defeasible logic is a rulebased nonmonotonic logic, with both strict and defeasible rules, and a priority relation on rules. We show that inference in the propositional form of the logic can be performed in linear time. This contrasts markedly with most other propositional nonmonotonic logics, i ..."
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Cited by 67 (6 self)
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Defeasible logic is a rulebased nonmonotonic logic, with both strict and defeasible rules, and a priority relation on rules. We show that inference in the propositional form of the logic can be performed in linear time. This contrasts markedly with most other propositional nonmonotonic logics, in which inference is intractable. 1 Introduction Mostwork in nonmonotonicreasoning has focussed on languages for whichpropositional inference is not tractable. Sceptical default reasoning is \Pi p 2 hard, even for very simple classes of default rules, as is sceptical autoepistemic reasoning and propositional circumscription. The complexity of sceptical inference from logic programs with negationasfailure varies according to the semantics of negation. For both the stable model semantics and the Clark completion, sceptical inference is coNPhard. See [13, 9] for more details. Although such languages are very expressive, and this expressiveness has been exploited in answerset progra...
Efficient Defeasible Reasoning Systems
 International Journal of Artificial Intelligence Tools
, 2001
"... For many years, the nonmonotonic reasoning community has focussed on highly expressive logics. Such logics have tumed out to be computationally expensive, and have given little support to the practical use of nonmonotonic reasoning. In this work we discuss defeasible logic, a lessexpressive but ..."
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Cited by 59 (20 self)
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For many years, the nonmonotonic reasoning community has focussed on highly expressive logics. Such logics have tumed out to be computationally expensive, and have given little support to the practical use of nonmonotonic reasoning. In this work we discuss defeasible logic, a lessexpressive but more efficient nonmonotonic logic. We report on two new implemented systems for defeasible logic: a query answering system employing a backwardchaining approach, and a forwardchaining implementation that computes all conclusions. Our experimental evaluation demonstrates that the systems can deal with large theories (up to hundreds of thousands of rules). We show that defeasible logic has linear complexity, which contrasts markedly with most other nonmonotonic logics and helps to explain the impressive experimental results. We believe that defeasible logic, with its eficiency and simplicity, is a good candidate to be used as a modelling language for practical applications, including modelling of regulations and business rules. 1
A flexible framework for defeasible logics
 In Proc. American National Conference on Artificial Intelligence (AAAI2000
, 2000
"... Logics for knowledge representation suffer from overspecialization: while each logic may provide an ideal representation formalism for some problems, it is less than optimal for others. A solution to this problem is to choose from several logics and, when necessary, combine the representations. In g ..."
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Cited by 56 (47 self)
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Logics for knowledge representation suffer from overspecialization: while each logic may provide an ideal representation formalism for some problems, it is less than optimal for others. A solution to this problem is to choose from several logics and, when necessary, combine the representations. In general, such an approach results in a very difficult problem of combination. However, if we can choose the logics from a uniform framework then the problem of combining them is greatly simplified. In this paper, we develop such a framework for defeasible logics. It supports all defeasible logics that satisfy a strong negation principle. We use logic metaprograms as the basis for the framework.
The KGP Model of Agency
 In Proc. ECAI2004
, 2004
"... This paper presents a new model of agency, called the KGP (Knowledge, Goals and Plan) model. This draws from the classic BDI model and proposes a hierarchical agent architecture with a highly modular structure that synthesises various reasoning and sensing capabilities of the agent in an open and dy ..."
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Cited by 54 (35 self)
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This paper presents a new model of agency, called the KGP (Knowledge, Goals and Plan) model. This draws from the classic BDI model and proposes a hierarchical agent architecture with a highly modular structure that synthesises various reasoning and sensing capabilities of the agent in an open and dynamic environment. The novel features of the model include: its innovative use of Computational Logic (CL) in a way that facilitates both the formal analysis of the model and its computational realisability directly from the highlevel specification of the agents (a first prototype for the development of KGP agents exists, based upon a correct computational counterpart of the model), the modular separation of concerns and flexibility afforded by the model in designing heterogeneous agents and in developing independently the various components of an agent, and the declarative agent control provided through a contextsensitive cycle CL theory component that regulates the agent's operational behaviour, according to the current circumstances of operation, thus breaking away from the conventional onesizefitsall control of operation.
Defeasible Logic versus Logic Programming without Negation as Failure
 JOURNAL OF LOGIC PROGRAMMING
, 2000
"... Recently there has been increased interest in logic programmingbased default reasoning approaches which are not using negationasfailure in their object language. Instead, default reasoning is modelled by rules and a priority relation among them. In this paper we compare the expressive power o ..."
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Cited by 47 (19 self)
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Recently there has been increased interest in logic programmingbased default reasoning approaches which are not using negationasfailure in their object language. Instead, default reasoning is modelled by rules and a priority relation among them. In this paper we compare the expressive power of two approaches in this family of logics: Defeasible Logic, and sceptical LPwNF. Our results show that the former has a strictly stronger expressive power. The difference is caused by the latter logic's failure to capture the idea of teams of rules supporting a specific conclusion.