CF2-extensions as answer-set models

Extension-based argumentation semantics have shown to be a suitable approach for performing practical reasoning. Since extension-based argumentation semantics were formalized in terms of relationships between atomic arguments, it has been shown that extension-based argumentation semantics based on admissible sets such as stable semantics can be characterized in terms of answer sets. In this paper, we present an approach for characterizing SCC-recursive semantics in terms of answer set models. In particular, we will show a characterization of CF2 in terms of answer set models. This result suggests that not only extension-based argumentation semantics based on admissible sets can be characterized in terms of answer sets; but also extension-based argumentation semantics based on Strongly Connected Components can be characterized in terms of answer sets.Peer ReviewedPreprin

An Implementation of Splitting for Dung Style Argumentation Frameworks

Argumentation and reasoning have been an area of research in such disciplines as philosophy, logic and artificial intelligence for quite some time now. In the area of AI, knowledge needed for reasoning can be represented using various kinds of representation systems. The natural problem posed by this fact is that of possible incompatibility between heterogeneous systems as far as communication between them is concerned. This imposes a limitation on the possibility of extending smaller knowledge bases to larger ones. In order to facilitate a common platform for exchange across the systems unified formalisms for the different approaches to knowledge representation are required. This was the motivation for Dung [11] to propose in his 1995 paper an approach that later came to be known as an abstract argumentation framework. Roughly speaking, Dung's arguments are abstract entities which are related to each other by the means of conflicts between them. An intuitive graphical representation of Dung style framework is a graph whose nodes stand for arguments and whose edges stand for conflicts. A framework postulated this way is on one hand too general to be used on its own, but on the other hand it is general enough as to allow for varied extensions increasing its expressiveness, which indeed have been proposed. They include value-based argumentation frameworks by Bench-Capon et al. [6], preference-based argumentation frameworks by Amgoud and Cayrol [1] and bipolar argumentation frameworks by Brewka and Woltran [7], to name a few. The present thesis is concerned with yet another variation of Dung's framework: the concept of splitting. It was developed by Baumann [4] with one of the underlying purposes being that the computation time in frameworks which have been split into two parts and then computed separately may show some improvement in comparison to their variant without splitting. It was one of the main tasks of my work to develop an efficient algorithm for the splitting operation based on the theoretical framework given in [4]. On the other hand I hoped to confirm the expectation that splitting can indeed make a computation perform better

Computing the Grounded Semantics in all the Subgraphs of an Argumentation Framework: an Empirical Evaluation

Given an argumentation framework – with a finite set of arguments and the attack relation identifying the graph – we study how the grounded labelling of a generic argument a varies in all the subgraphs of . Since this is an intractable problem of above-polynomial complexity, we present two non-naïve algorithms to find the set of all the subgraphs where the grounded semantic assigns to argument a specific label . We report the results of a series of empirical tests over graphs of increasing complexity. The value of researching the above problem is two-fold. First, knowing how an argument behaves in all the subgraphs represents strategic information for arguing agents. Second, the algorithms can be applied to the computation of the recently introduced probabilistic argumentation frameworks

Algorithms for Dynamic Argumentation Frameworks: An Incremental SAT-Based Approach

Peer reviewe

Dynamics in Abstract Argumentation Frameworks with Recursive Attack and Support Relations

Argumentation is an important topic in the field of AI. There is a substantial amount of work about different aspects of Dung's abstract Argumentation Framework (AF). Two relevant aspects considered separately so far are extending the framework to account for recursive attacks and supports, and considering dynamics, i.e., AFs evolving over time. In this paper, we jointly deal with these two aspects.We focus on Attack-Support Argumentation Frameworks (ASAFs) which allow for attack and support relations not only between arguments but also targeting attacks and supports at any level, and propose an approach for the incremental computation of extensions (sets of accepted arguments, attacks and supports) of updated ASAFs. Our approach assumes that an initial ASAF extension is given and uses it for first checking whether updates are irrelevant; for relevant updates, an extension of an updated ASAF is computed by translating the problem to the AF domain and leveraging on AF solvers. We experimentally show our incremental approach outperforms the direct computation of extensions for updated ASAFs.Fil: Alfano, Gianvincenzo. Universita Della Calabria.; ItaliaFil: Cohen, Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Ciencias e Ingeniería de la Computación. Universidad Nacional del Sur. Departamento de Ciencias e Ingeniería de la Computación. Instituto de Ciencias e Ingeniería de la Computación; ArgentinaFil: Gottifredi, Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Ciencias e Ingeniería de la Computación. Universidad Nacional del Sur. Departamento de Ciencias e Ingeniería de la Computación. Instituto de Ciencias e Ingeniería de la Computación; ArgentinaFil: Greco, Sergio. Universita Della Calabria.; ItaliaFil: Parisi, Francesco. Universita Della Calabria.; ItaliaFil: Simari, Guillermo R.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Ciencias e Ingeniería de la Computación. Universidad Nacional del Sur. Departamento de Ciencias e Ingeniería de la Computación. Instituto de Ciencias e Ingeniería de la Computación; Argentina24th European Conference on Artificial IntelligenceSantiago de CompostelaEspañaEuropean Association for Artificial IntelligenceUniversidad de Santiago de Compostel

An Efficient Java-Based Solver for Abstract Argumentation Frameworks: jArgSemSAT

Dung’s argumentation frameworks are adopted in a variety of applications, from argument-mining, to intelligence analysis and legal reasoning. Despite this broad spectrum of already existing applications, the mostly adopted solver—in virtue of its simplicity—is far from being comparable to the current state-of-the-art solvers. On the other hand, most of the current state-of-the-art solvers are far too complicated to be deployed in real-world settings. In this paper we provide and extensive description of jArgSemSAT, a Java re-implementation of ArgSemSAT. ArgSemSAT represents the best single solver for argumentation semantics with the highest level of computational complexity. We show that jArgSemSAT can be easily integrated in existing argumentation systems (1) as an off-the-shelf, standalone, library; (2) as a Tweety compatible library; and (3) as a fast and robust web service freely available on the Web. Our large experimental analysis shows that—despite being written in Java—jArgSemSAT would have scored in most of the cases among the three bests solvers for the two semantics with highest computational complexity—Stable and Preferred—in the last competition on computational models of argumentation

Argumentation and graph properties

Argumentation theory is an area of interdisciplinary research that is suitable to characterise several diverse situations of reasoning and judgement in real world practices and challenges. In the discipline of Artificial Intelligence, argumentation is formalised by reasoning models based on building and evaluation of interacting arguments. In this argumentation framework, the semantics of acceptance plays a fundamental role in the argument evaluation process. The determination of accepted arguments under a given semantics (admissible, preferred, stable, etc.) can be a time-consuming and tedious (in number of steps) process. In this work we try to overcome this substantial process by providing a method to compute accepted arguments from an argumentation framework. The principle of this method is to combine mathematical properties (e.g. symmetry, asymmetry, strong connectivity and irreflexivity) of graphs built from the argumentation system to compute sets of accepted arguments. In this work, we combine several graph properties to provide three main propositions; one for identifying accepted arguments under the admissible, preferred semantics and the other to easily identify stable extension. The proofs of the suggested propositions are detailed and this is part of an approach designed to increase collaborative decision-making by improving the effectiveness of reasoning processes

Äquivalenz schwach expandierter Argumentationsframeworks in ausgewählten Semantiken

In dieser Arbeit haben wir uns mit der Äquivalenz schwach expandierter Argumentationsframeworks beschäftigt. Zunächst haben wir nochmal die Grundlagen der formalen Argumentation und der Semantiken der Akzeptierbarkeit wiederholt. Anschließend betrachteten wir die Konzepte der Expansionen und Splittings und konnten einen direkten Zusammenhang zwischen diesen feststellen. Daraufhin wandten wir uns den Splitting-Resultaten von Baumann [3] zu. Wir haben Redukte und Modifikationen kennengelernt und gesehen wie man diese zur Berechnung neuer Extensionen verwenden kann, nachdem ein Argumentationframework expandiert wurde. Dies geschieht durch das Berechnen einer Extension des ursprünglichen Frameworks, das Ermitteln der Modifikation des Redukts der Erweiterung und deren Extension und anschließende Vereinigung der beiden Extensionen zu einer neuen Extension des Gesamtframeworks

On the responsibility for undecisiveness in preferred and stable labellings in abstract argumentation

Different semantics of abstract Argumentation Frameworks (AFs) provide different levels of decisiveness for reasoning about the acceptability of conflicting arguments. The stable semantics is useful for applications requiring a high level of decisiveness, as it assigns to each argument the label “accepted” or the label “rejected”. Unfortunately, stable labellings are not guaranteed to exist, thus raising the question as to which parts of AFs are responsible for the non-existence. In this paper, we address this question by investigating a more general question concerning preferred labellings (which may be less decisive than stable labellings but are always guaranteed to exist), namely why a given preferred labelling may not be stable and thus undecided on some arguments. In particular, (1) we give various characterisations of parts of an AF, based on the given preferred labelling, and (2) we show that these parts are indeed responsible for the undecisiveness if the preferred labelling is not stable. We then use these characterisations to explain the non-existence of stable labellings. We present two types of characterisations, based on labellings that are more (or equally) committed than the given preferred labelling on the one hand, and based on the structure of the given AF on the other, and compare the respective AF parts deemed responsible. To prove that our characterisations indeed yield responsible parts, we use a notion of enforcement of labels through structural revision, by means of which the preferred labelling of the given AF can be turned into a stable labelling of the structurally revised AF. Rather than prescribing how this structural revision is carried out, we focus on the enforcement of labels and leave the engineering of the revision open to fulfil differing requirements of applications and information available to users