A Plausibility Semantics for Abstract Argumentation Frameworks

We propose and investigate a simple ranking-measure-based extension semantics for abstract argumentation frameworks based on their generic instantiation by default knowledge bases and the ranking construction semantics for default reasoning. In this context, we consider the path from structured to logical to shallow semantic instantiations. The resulting well-justified JZ-extension semantics diverges from more traditional approaches.Comment: Proceedings of the 15th International Workshop on Non-Monotonic Reasoning (NMR 2014). This is an improved and extended version of the author's ECSQARU 2013 pape

A Theory of Partitioned Global Address Spaces

Partitioned global address space (PGAS) is a parallel programming model for the development of applications on clusters. It provides a global address space partitioned among the cluster nodes, and is supported in programming languages like C, C++, and Fortran by means of APIs. In this paper we provide a formal model for the semantics of single instruction, multiple data programs using PGAS APIs. Our model reflects the main features of popular real-world APIs such as SHMEM, ARMCI, GASNet, GPI, and GASPI. A key feature of PGAS is the support for one-sided communication: a node may directly read and write the memory located at a remote node, without explicit synchronization with the processes running on the remote side. One-sided communication increases performance by decoupling process synchronization from data transfer, but requires the programmer to reason about appropriate synchronizations between reads and writes. As a second contribution, we propose and investigate robustness, a criterion for correct synchronization of PGAS programs. Robustness corresponds to acyclicity of a suitable happens-before relation defined on PGAS computations. The requirement is finer than the classical data race freedom and rules out most false error reports. Our main result is an algorithm for checking robustness of PGAS programs. The algorithm makes use of two insights. Using combinatorial arguments we first show that, if a PGAS program is not robust, then there are computations in a certain normal form that violate happens-before acyclicity. Intuitively, normal-form computations delay remote accesses in an ordered way. We then devise an algorithm that checks for cyclic normal-form computations. Essentially, the algorithm is an emptiness check for a novel automaton model that accepts normal-form computations in streaming fashion. Altogether, we prove the robustness problem is PSpace-complete

Cut-Simulation and Impredicativity

We investigate cut-elimination and cut-simulation in impredicative (higher-order) logics. We illustrate that adding simple axioms such as Leibniz equations to a calculus for an impredicative logic -- in our case a sequent calculus for classical type theory -- is like adding cut. The phenomenon equally applies to prominent axioms like Boolean- and functional extensionality, induction, choice, and description. This calls for the development of calculi where these principles are built-in instead of being treated axiomatically.Comment: 21 page

Perspectives in Argumentation and Communication: A relevance-theoretic approach

The present paper presents an overview of the theories of relevance (Sperber&Wilson 1985, 1995, 1998, 2002; Wilson & Sperber 2002) with a particular focus on argumentation and human communication. An in-depth analysis of the human communication plays a critical role in accounting for the theory of relevance. Standing in opposition to the traditional model whereby the communication is accomplished by the transmission of an intended message from a sending party to the receiver through a channel, which, in turn, is decoded and some type of signal or feedback is sent back, the Relevance theorists argue that what distinguishes an input from others is its relevance to the receiver since every utterance creates in the addressee an expectation of relevance. Yus (2006) also relates Relevance Theory to human communication since it is established within a broader cognitive framework, which, in turn, makes humans tend to maximize the relevance of the utterance. This paper will contribute to a better understanding of RT as a general linguistic principle organizing the goal-oriented use of language in communication. Any form of communication can hardly be achieved without contributing factors such as relevance, coherence, semantic interconnectedness and intertextuality. In this regard, we will attempt to study the role of relevance in pragmatics, semantics and communication. We end by taking into account the relevance-theoretic model for achieving a successful communication. Keywords: theory of relevance, argumentation, communication, coherence, pragmatics

A model to support collective reasoning: Formalization, analysis and computational assessment

Inspired by e-participation systems, in this paper we propose a new model to represent human debates and methods to obtain collective conclusions from them. This model overcomes drawbacks of existing approaches by allowing users to introduce new pieces of information into the discussion, to relate them to existing pieces, and also to express their opinion on the pieces proposed by other users. In addition, our model does not assume that users' opinions are rational in order to extract information from it, an assumption that significantly limits current approaches. Instead, we define a weaker notion of rationality that characterises coherent opinions, and we consider different scenarios based on the coherence of individual opinions and the level of consensus that users have on the debate structure. Considering these two factors, we analyse the outcomes of different opinion aggregation functions that compute a collective decision based on the individual opinions and the debate structure. In particular, we demonstrate that aggregated opinions can be coherent even if there is a lack of consensus and individual opinions are not coherent. We conclude our analysis with a computational evaluation demonstrating that collective opinions can be computed efficiently for real-sized debates

Commentary on: Assimakis Tseronis\u27 Argumentative functions of visuals: Beyond claiming and justifying

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Graph Models for Rational Social Interaction

A fundamental issue in multi-agent systems is to extract a consensus from a group of agents with different perspectives. Even if the bilateral relationships (reflecting the outcomes of disputes, product comparisons, or evaluation of political candidates) are rational, the collective output may be irrational (e.g., intransitivity of group preferences). This motivates AI’s research for devising social outcomes compatible with individual positions. Frequently, such situations are modeled as graphs. While the preponderance of formal theoretical studies of such graph based-models has addressed semantic concerns for defining a desirable output in order to formalize some high-level intuition, results relating to algorithmic and computational complexity are also of great significance from the computational point of view. The first Part of this thesis is devoted to combinatorial aspects of Argumentation Frameworks related to computational issues. These abstract frameworks, introduced by Dung in 1995, are directed graphs with nodes interpreted as arguments and the directed edges as attacks between the arguments. By designing a conflict-resolution formalism to make distinction among acceptable and unacceptable arguments, Dung initiated an important area of research in Artificial Intelligence. I prove that any argumentation framework can be syntactically augmented into a normal form preserving the semantic properties of the original arguments, by using a cubic time rewriting technique. I introduce polyhedral labellings for an argumentation frameworks, which is a polytope with the property that its integral points are exactly the incidence vectors of specific types of Dung’s outcome. Also, a new notion of acceptability of arguments is considered – deliberative acceptability – and I provide it’s time computational complexity analysis. This part extends and improves some of the results from the my Master thesis. In the second Part, I introduce a novel graph-based model for aggregating preferences. By using graph operations to describe properties of the aggregators, axiomatic characterizations of aggregators corresponding to usual majority or approval & disapproval rule are given. Integrating Dung’s semantics into our model provides a novel qualitative approach to classical social choice: argumentative aggregation of individual preferences. Also, a functional framework abstracting many-to-many two-sided markets is considered: the study of the existence of a Stable Choice Matching in a Bipartite Choice System is reduced to the study of the existence of Stable Common Fixed Points of two choice functions. A generalization of the Gale-Shapley algorithm is designed and, in order to prove its correctness, a new characterization of path independence choice functions is given. Finally, in the third Part, we extend Dung’s Argumentation Frameworks to Opposition Frameworks, reducing the gap between Structured and Abstract Argumentation. A guarded attack calculus is developed, giving proper generalizations of Dung’s extensions.Ein grundlegendes Problem von Multiagentensystemen ist, eine Gruppe von Agenten mit unterschiedlichen Perspektiven zum Konsens zu bringen.W¨ahrend die bilaterale Ergebnisse von Rechtsstreitigkeiten, Produktvergleichen sowie die Bewertung von politischen Kandidaten wiederspiegelnden Beziehungen rational sein sollten, k¨onnte der kollektive Ausgang irrational sein z.B. durch die Intransitivit¨at von Pr¨aferenzen der Gruppe. Das motiviert die KI-Forschung zur Entwicklung von sozialen Ergebnissen, welche mit individuellen Einstellungen kompatibel sind. H¨aufig werden solche Situationen als Graphen modelliert. W¨ahrend die meisten formalen theoretischen Studien von Graphmodellen sich mit semantischen Aspekten f¨ur die Definition eines w¨unschenswerten Ausgangs zur Formalisierung auf hohem Intuitionsniveau besch¨aftigen, ist es ebenfalls von großer Bedeutung, die Komplexit¨at von Algorithmen und Berechnungen zu verstehen. Der erste Teil der vorliegenden Arbeit widmet sich den kombinatorischen Aspekten von Argumentation Frameworks im Zusammenhang mit rechnerischen Fragen. Diese von Dung in 1995 eingef ¨uhrten abstrakten Frameworks sind gerichtete Graphen mit als Argumenten zu interpretierenden Knoten, wobei die gerichteten Kanten Angriffe zwischen den Argumenten sind. Somit hat Dung mit seiner Gestaltung eines Konfliktl¨osungsformalismus zur Unterscheidung zwischen akzeptablen und inakzeptablen Argumenten f¨ur einen wichtigen Bereich von Forschung in KI den Grundstein gelegt. Die Verfasserin hat bewiesen, dass jedes Argumentation Framework sich in einer die semantischen Eigenschaften der originalen Argumente bewahrenden normalen Form syntaktisch erweitern l¨asst, indem man eine mit kubischer Laufzeit umwandelnde Technik verwendet. Neu eingef¨urt werden hier Polyhedrische Etiketten f¨ur Argumentation Frameworks. Dabei handelt es sich um einen Polytop, wessen ganze Punkte genau die Inzidenzvektoren von bestimmten Arten von Dungs Ausgabe sind. Weiterhin wird ein neuer Begriff der Akzeptanz von Argumenten gepr¨agt, n¨amlich - deliberative Akzeptanz - und dessen Komplexit¨at analysiert. Dieser Teil erweitert und verfeinert einige ihrer Ergebnisse aus der Masterarbeit. Im zweiten Teil wurde ein neuartiges graphenbasiertes Modell f¨ur die Aggregation von Pr¨aferenzen erarbeitet. Hier werden axiomatische Charakterisierungen von Aggregatoren neu eingef¨uhrt, und zwar durch die Verwendung von Graphoperationen zur Beschreibung der Eigenschaften von Aggregatoren. Sie entsprechen dem ¨ublichen Mehrheitsprinzip bzw. der Genehmigungs- & Ablehnungsregel. Einen neuartigen, qualitativen Ansatz im Vergleich zu der klassischen Sozialwahltheorie bietet die Integration der Semantik von Dung in dem neuen Modell, und zwar argumentative Aggregation individueller Pr¨aferenzen. Desweiteren wird ein funktionales many to many zweiseitige M¨arkte abstrahierendes Framework untersucht, indem statt die Existenz einer Stabilen Wahl Matching in einem Bipartite Wahlsystem zu studieren, wird die Existenz von Stable Common Fixed Points auf zwei Wahlfunktionen erforscht. Im n¨achsten Schritt wird eine neue Verallgemeinerung des Gale-Shapley Algorithmus entworfen und eine neue Charakterisierung der Wegunabh¨angigkeitsfunktion gegeben, die einen Korrektheitsbeweis f¨ur den Algorithmus erm¨oglicht. Im dritten Teil werden schließlich Dungs Argumentation Frameworks auf Opposition Frameworks erweitert und dadurch die in der gegenw¨artigen Forschung bestehende L¨ucke zwischen strukturierter und abstrakter Argumentation verringert. Daf¨ur wird ein bewachter Angriffskalk¨ul entwickelt, welches strikten Verallgemeinerungen von Dungs echten Erweiterungen f¨uhrt

Solving stable matching problems using answer set programming

Since the introduction of the stable marriage problem (SMP) by Gale and Shapley (1962), several variants and extensions have been investigated. While this variety is useful to widen the application potential, each variant requires a new algorithm for finding the stable matchings. To address this issue, we propose an encoding of the SMP using answer set programming (ASP), which can straightforwardly be adapted and extended to suit the needs of specific applications. The use of ASP also means that we can take advantage of highly efficient off-the-shelf solvers. To illustrate the flexibility of our approach, we show how our ASP encoding naturally allows us to select optimal stable matchings, i.e. matchings that are optimal according to some user-specified criterion. To the best of our knowledge, our encoding offers the first exact implementation to find sex-equal, minimum regret, egalitarian or maximum cardinality stable matchings for SMP instances in which individuals may designate unacceptable partners and ties between preferences are allowed. This paper is under consideration in Theory and Practice of Logic Programming (TPLP).Comment: Under consideration in Theory and Practice of Logic Programming (TPLP). arXiv admin note: substantial text overlap with arXiv:1302.725

A hybrid model of electronic negotiation : integration of negotiation support and automated negotiation models

Electronic business negotiations are enabled by different electronic negotiation models: automated negotiation models for software agents, negotiation support models for human negotiators, and auction models for both. To date, there is no electronic negotiation model that enables bilateral multi-issue negotiations between a human negotiator and a negotiation agent?an important task in electronic negotiation research. In this thesis, a model is presented that integrates the automated negotiation model and the negotiation support model. The resulting hybrid negotiation model paves the way for human-agent business negotiations. The integration of two models is realised at the levels of negotiation process, communication support and decision making. To this end, the negotiation design, negotiation process, negotiation decision making, and negotiation communication in negotiation support systems (NSSs) and agent negotiation systems (ANSs) are studied and analysed. The analyses on these points help in strengthening the motivation behind hybrid negotiation model and setting aims for the integration of an NSS and an ANS in hybrid negotiation model. We mainly propose a human-agent negotiation design, negotiation process protocols to support the design, a hybrid communication model for human-agent interaction, an agent decision-making model for negotiation with human, and a component for interoperability between NSS and ANS. The agent decision-making model is composed of heuristic and argumentation-based negotiation techniques. It is proposed after analysing different automated negotiation models for different human negotiation strategies. The proposed communication model supports human negotiator and negotiation agent to understand and process negotiation messages from each other. This communication model consists of negotiation ontology, a wrapper agent, and a proper selection of an agent communication language (ACL) and a content language. The wrapper agent plays a role for interoperability between agent system and NSS by providing a communication interface along with the negotiation ontology. The negotiation ontology, ACL and agent content language make the communication model of negotiation agent in ANS. The proposed hybrid model is realised by integrating an ANS into NSS Negoisst. The research aim is to show that a hybrid negotiation system, composed of two heterogeneous negotiation models, can enable human-agent multi-issue integrative negotiations.Elektronische ökonomische Verhandlungen werden durch verschiedene Verhandlungsmodelle ermöglicht: Automatisierte Verhandlungsmodelle für Softwareagenten, Verhandlungsunterstützung für menschliche Verhandelnde und Auktionsmodelle für Beide. Bis heute existiert kein elektronisches Verhandlungsmodell, das bilaterale multi-attributive Verhandlungen zwischen einem menschlichen Verhandelnden und einem Verhandlungsagenten ? eine wichtige Aufgabe in der Forschung im Bereich elektronischer Verhandlungen. In dieser Arbeit wird ein Modell präsentiert, welches das automatisierte Verhandlungsmodell und das Verhandlungsunterstützungsmodell integriert. Das resultierende hybride Verhandlungsmodell ebnet den Weg für ökonomische Mensch-Agent-Verhandlungen. Die Integration der zwei Modelle ist realisiert auf der Ebene von Verhandlungsprozess, Kommunikationsunterstützung und Entscheidungsunterstützung. Dazu werden Verhandlungsdesign, Verhandlungsprozess, verhandlungsbezogene Entscheidungsfindung und Verhandlungskommunikation in Verhandlungsunterstützungssystemen (NSS) und Agentenverhandlungssystemen (ANS) studiert und analysiert. Die Analysen zu diesen Punkten verstärken die Motivation hinter dem hybriden Verhandlungsmodell und bestimmen die Ziele für die Integration von NSS und ANS. Es werden hauptsächlich ein Mensch-Agent-Verhandlungsdesign, Verhandlungsprozessprotokolle zur Unterstützung des Designs, ein hybrides Kommunikationsmodell für Mensch-Agent-Kommunikation, ein Agenten-Entscheidungsmodell für die Verhandlung mit menschlichem Gegenpart und eine Komponente für die Interoperabilität zwischen NSS und ANS. Das Entscheidungsmodell für Agenten besteht aus heuristischen und argumentativen Verhandlungstechniken. Es wird aufgestellt nachdem verschiedene automatisierte Verhandlungsmodelle für verschiedene menschliche Verhandlungsstrategien analysiert worden sind. Die vorgeschlagenen Kommunikationsmodelle unterstützen menschliche Verhandler und Verhandlungsagenten dabei Verhandlungsnachrichten voneinander zu verstehen und zu verarbeiten. Dieses Kommunikationsmodell besteht aus einer Verhandlungsontologie, einem Wrapper-Agenten und einer angemessenen Auswahl der Agentenkommunikationssprache (ACL) und der Inhaltssprache. Der Wrapper-Agent spielt eine Rolle bei der Interoperabilität zwischen dem Agentensystem und dem NSS durch eine Kommunikationsschnittstelle zusammen mit der Verhandlungsontologie. Die Verhandlungsontologie, die ACL und die Inhaltssprache der Agenten ergeben das Kommunikationsmodell der Verhandlungsagenten im ANS. Das vorgestellte hybride Modell ist realisiert als Integration eines ANS in das NSS Negoisst. Das Forschungsziel ist zu zeigen, dass ein hybrides Verhandlungssystem, basierend auf zwei heterogenen Verhandlungsmodellen, integrative multi-attributive Mensch-Agent-Verhandlungen ermöglicht