Argumentation Semantics for Defeasible Logics

Lecture Notes in Computer Science

Satoh

et al. 2012

Abstract. Speculative Computation is an effective means for solving problems with incomplete information in an open and distributed environment, such as peer-to-peer environment. It allows such a system to compute tentative (and possibly final) solutions using default knowledge about the current environment, or the agent's perception, even if the communications between peers are delayed or broken. However, previous work in speculative reasoning assumed that agents are hierarchically structured, which may not be the case in reality. We propose a more general multi-agents system with no centralized control. Agents in the framework have equivalent functionalities and can collaborate with each other to achieve their common goals. We characterize the framework using the argumentation semantics of defeasible logic, which provides support of speculative reasoning in the presence of conflicting information. We provide an operational model for the framework and present a prototype implementation of the model.

“…It is based on the argumentation semantics of DL presented in Governatori et al [10] with the notion of askable literals and preference among system contexts. Definition 1.…”

Section: Defeasible Speculative Reasoning Frameworkmentioning

confidence: 99%

“…In [10], Governatori et al describe DL and its variants in argumentation theoretic terms, on which this paper is based.…”

Section: An Informal Introduction To Defeasible Logicmentioning

confidence: 99%

Distributed Defeasible Speculative Reasoning in Ambient Environment

Lam

Lecture Notes in Computer Science

Satoh

et al. 2012

“…DL is characterised by an argumentation semantics [3] and also has several efficient implementations [2]. Temporal Defeasible Logic (TDL) is an umbrella expression to designate extensions of DL to capture time.…”

Section: Temporal Defeasible Logicmentioning

confidence: 99%

Variants of temporal defeasible logics for modelling norm modifications

Proceedings of the 11th International Conference on Artificial Intelligence and Law

Rotolo

Riveret

et al. 2007

This paper proposes some variants of Temporal Defeasible Logic (TDL) to reason about normative modifications. These variants make it possible to differentiate cases in which, for example, modifications at some time change legal rules but their conclusions persist afterwards from cases where also their conclusions are blocked. BACKGROUND AND MOTIVATIONThis paper presents some variants of Temporal Defeasible Logic (TDL) [5,4] to reason about different aspects of norm modifications. The issues discussed in this paper are similar to those assumed in [5], namely: (1) to reason about conditional modifications of conditional normative provisions, where the former ones apply under, and are conditioned to, the occurrence of some uncertain events; (2) to identify criteria for detecting and solving conflicts between textual modifications; (3) to clarify the specific role played by the temporal dimension in modelling norm modification processes. The novelty of this work is that we are interested in defining different temporal constraints according to which the elements of a normative system, and the conclusions that follow from them, can, or cannot persist over time. Indeed, several options are available, and each of them corresponds to a specific way through which norm modifications can take place and behave.Norm applications and modifications take place along the axis of time. In particular, a rule is represented at least as (a t ⇒ b t ) : t , where instants t and t indicate the time at which a and b hold, while t is the time when the rule is in force. A temporal model should allow us to give an accurate account of the dynamics of norms and therefore to manage legal modifications consistently with legal principles [10].A legal system is defined as a set of documents fixed at a time t and which have been issued by an authority and whose validity de- * Supported by the Australian Research Council under the Discovery Project DP0558854.† Supported by the European project for Standardized Transparent Representations in order to Extend Legal Accessibility (ES-TRELLA, IST-4-027655).Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. pends on rules that determine, for any given time, whether a single document belongs to the system. Formally:where m ∈ N, D i denotes documents and t is a fixed time in a discrete representation. A normative system, in turn, takes the documents belonging to a legal system and organises them to reflect their evolution over time. A normative system should therefore be defined as a particular discrete time-series of legal syst...

“…In the last few years DL has been applied in many fields; in addition DL encompasses other existing formalisms proposed in the AI & Law field such as Prakken and Sartor's [21] and Loui and Simari's [25] (see, [9]), and recent work shows that DL is suitable for extensions with modal and deontic operators [10] and violations which in turn allows DL to be used to represent and reason with business contracts [11,8]. Here we propose a non-monotonic logic of institutional agency based on the framework for DL developed in [1].…”

Section: The Systemmentioning

confidence: 99%

Temporalised normative positions in defeasible logic

Proceedings of the 10th International Conference on Artificial Intelligence and Law

Rotolo

Sartor

2005

109

We propose a computationally oriented non-monotonic multi-modal logic arising from the combination of temporalised agency and temporalised normative positions. We argue about the defeasible nature of these notions and then we show how to represent and reason with them in the setting of Defeasible Logic. MOTIVATION AND LAYOUTAn increasing number of works on agents assume that in artificial societies normative concepts may play a decisive role, allowing for the flexible co-ordination of autonomous agents [5,20,15]. In particular, it seems crucial to model organisations of agents in terms of policy-based normative systems; accordingly an organisation should be characterised by specifying the normative positions relevant to design its structure. These positions include duties, permissions, but also powers, as for instance powers of creating further normative positions on the head of other agents. In this paper we will develop a formal machinery to account for several fundamental concepts that are required to model policy-based normative systems. These concepts will be embedded in a nonmonotonic and computationally-oriented framework based on Defeasible Logic (DL).From the conceptual standpoint, it is well known that the basic deontic qualifications (obligatory, forbidden, permitted and facultative) are not sufficient to capture all fundamental normative notions, such as the concepts of rights and power. For this reason, we will first provide an account in DL of the notion of other-directed obligation [14] to express, e.g., the first Hohfeldian set of fundamental concepts: duty, right, noright, and privilege. Second, we shall focus on different kinds of normative conditionals. This will enable us to characterise also the idea of normative power and articulate many potestative concepts such as the second Hohfeldian set of concepts: power, liability (or, subjection, to avoid confusion with the notion of liability, as used in tort law), disability, and immunity. * This work was partially supported by Australia Research Council under Discovery Project No. DP0558854 on "A Formal Approach to Resource Allocation in Web Service Oriented Composition in Open Marketplaces". Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. In general, we shall see how the analysis of normative conditionality and normative positions has to include temporal aspects in order to capture a number of nuances in the perspective of framing a fine-grained classification of such concepts. In fact, normative determinations take place along the axis of time: Normative preconditions hold or happen in certain temporally characterised occasions, and consequently their effects too hold or happen wi...