Pietro Baroni

AIJ Journal 2024 Journal Article

On generalized notions of consistency and reinstatement and their preservation in formal argumentation

• Pietro Baroni
• Federico Cerutti
• Massimiliano Giacomin

We present a conceptualization providing an original domain-independent perspective on two crucial properties in reasoning: consistency and reinstatement. They emerge as a pair of dual characteristics, representing complementary requirements on the outcomes of reasoning processes. Central to our formalization are two underlying parametric relations: incompatibility and reinstatement violation. Different instances of these relations give rise to a spectrum of consistency and reinstatement scenarios. As a demonstration of versatility and expressive power of our approach we provide a characterization of various abstract argumentation semantics which are expressed as combinations of distinct consistency and reinstatement constraints. Moreover, we conduct an investigation into preserving these essential properties across different reasoning stages. Specifically, we delve into scenarios where a labelling is derived from other labellings through a synthesis function, using the synthesis of argument justification as an illustrative instance. We achieve a general characterization of consistency preservation synthesis functions, while we unveil an impossibility result concerning reinstatement preservation, leading us to explore an alternative notion to ensure feasibility. Our exploration reveals a weakness in the traditional definition of argument justification, for which we propose a refined version overcoming this limitation.

FLAP Journal 2023 Journal Article

Decomposing Semantics in Abstract Argumentation.

• Pietro Baroni
• Federico Cerutti
• Massimiliano Giacomin

The paper introduces a general model for the investigation on decomposability in abstract argumentation, i.e. the possibility of determining the labellings prescribed by a semantics based on evaluations of local functions in subframeworks. By exploiting this model, the paper shows the range of decomposable semantics with varying degrees of local information. A constructive procedure for identifying local functions is then devised, encompassing two kinds of local functions, both of them able to enforce decomposability whenever the semantics is decomposable. As an example of application, the decomposability properties of stable, grounded and preferred semantics are analyzed when local information concerning close neighbors is available.

FLAP Journal 2023 Journal Article

Explaining Classifiers' Outputs with Causal Models and Argumentation.

• Antonio Rago
• Fabrizio Russo
• Emanuele Albini
• Francesca Toni
• Pietro Baroni

We introduce a conceptualisation for generating argumentation frameworks (AFs) from causal models for the purpose of forging explanations for models’ outputs. The conceptualisation is based on reinterpreting properties of semantics of AFs as explanation moulds, which are means for characterising argumentative relations. We demonstrate our methodology by reinterpreting the property of bi-variate reinforcement in bipolar AFs, showing how the extracted bipolar AFs may be used as relation-based explanations for the outputs of causal models. We then evaluate our method empirically when the causal models represent (Bayesian and neural network) machine learning models for classification. The results show advantages over a popular approach from the literature, both in highlighting specific relationships between feature and classification variables and in generating counterfactual explanations with respect to a commonly used metric.

KR Conference 2022 Conference Paper

Explaining Causal Models with Argumentation: the Case of Bi-variate Reinforcement

• Antonio Rago
• Pietro Baroni
• Francesca Toni

Causal models are playing an increasingly important role in machine learning, particularly in the realm of explainable AI. We introduce a conceptualisation for generating argumentation frameworks (AFs) from causal models for the purpose of forging explanations for the models’ outputs. The conceptualisation is based on reinterpreting desirable properties of semantics of AFs as explanation moulds, which are means for characterising the relations in the causal model argumentatively. We demonstrate our methodology by reinterpreting the property of bi-variate reinforcement as an explanation mould to forge bipolar AFs as explanations for the outputs of causal models. We perform a theoretical evaluation of these argumentative explanations, examining whether they satisfy a range of desirable explanatory and argumentative properties.

IJCAI Conference 2021 Conference Paper

Argumentative XAI: A Survey

• Kristijonas Čyras
• Antonio Rago
• Emanuele Albini
• Pietro Baroni
• Francesca Toni

Explainable AI (XAI) has been investigated for decades and, together with AI itself, has witnessed unprecedented growth in recent years. Among various approaches to XAI, argumentative models have been advocated in both the AI and social science literature, as their dialectical nature appears to match some basic desirable features of the explanation activity. In this survey we overview XAI approaches built using methods from the field of computational argumentation, leveraging its wide array of reasoning abstractions and explanation delivery methods. We overview the literature focusing on different types of explanation (intrinsic and post-hoc), different models with which argumentation-based explanations are deployed, different forms of delivery, and different argumentation frameworks they use. We also lay out a roadmap for future work.

IJCAI Conference 2020 Conference Paper

Relation-Based Counterfactual Explanations for Bayesian Network Classifiers

• Emanuele Albini
• Antonio Rago
• Pietro Baroni
• Francesca Toni

We propose a general method for generating counterfactual explanations (CFXs) for a range of Bayesian Network Classifiers (BCs), e. g. single- or multi-label, binary or multidimensional. We focus on explanations built from relations of (critical and potential) influence between variables, indicating the reasons for classifications, rather than any probabilistic information. We show by means of a theoretical analysis of CFXs’ properties that they serve the purpose of indicating (potentially) pivotal factors in the classification process, whose absence would give rise to different classifications. We then prove empirically for various BCs that CFXs provide useful information in real world settings, e. g. when race plays a part in parole violation prediction, and show that they have inherent advantages over existing explanation methods in the literature.

JAIR Journal 2019 Journal Article

Enhancing Statement Evaluation in Argumentation via Multi-labelling Systems

• Pietro Baroni
• Regis Riveret

In computational models of argumentation, the justification of statements has drawn less attention than the construction and justification of arguments. Significant losses of sensitivity or expressibility on statement statuses can be incurred by otherwise appealing formalisms. In order to reappraise statement statuses and, more generally, to support a uniform modelling of different phases of the argumentation process we introduce multi-labelling systems, a generic formalism devoted to represent reasoning processes consisting of a sequence of labelling stages. In the argumentation context, two families of multi-labelling systens, called argument-focused and statement-focused approach are identified and compared. Then they are shown to be able to encompass several prominent literature proposals as special cases, thereby enabling a systematic comparison evidencing their merits and limits. Further, we show that the proposed model supports tunability of statement justification by specifying a few alternative statement justification labellings, and we illustrate how they can be seamlessly integrated into different formalisms.

AIJ Journal 2018 Journal Article

A general semi-structured formalism for computational argumentation: Definition, properties, and examples of application

• Pietro Baroni
• Massimiliano Giacomin
• Beishui Liao

In the field of computational argumentation several formalisms featuring different levels of abstraction and focusing on different aspects of the argumentation process have been developed. Their combined use, necessary to achieve a comprehensive formal coverage of the argumentation phenomenon, gives rise to a nontrivial interplay between different abstraction levels, so that counterintuitive or undesirable outcomes may result from the combination of formalisms which appear to be well-behaved when considered in isolation. To address this problem we introduce a semi-structured formalism for argumentation, called LAF-ensembles, capturing a set of essential features of structured arguments and define a class of set based argumentation frameworks appropriate to support a semantic assessment of arguments for LAF-ensembles. It is shown that, under suitable assumptions, the combination of a LAF-ensemble and of an appropriate argumentation framework is guaranteed to produce justification outcomes satisfying a set of essential requirements. The generality and usefulness of the proposed approach are demonstrated by illustrating its ability to capture as instances and enhance two structured argumentation formalisms from the literature, namely Vreeswijk's abstract argument systems and Modgil and Prakken's ASPIC +. In particular, a revised version of the latter formalism, properly dealing with generic contrariness and solving significant technical limitations of ASPIC +, is proposed.

AAAI Conference 2018 Conference Paper

How Many Properties Do We Need for Gradual Argumentation?

• Pietro Baroni
• Antonio Rago
• Francesca Toni

The study of properties of gradual evaluation methods in argumentation has received increasing attention in recent years, with studies devoted to various classes of frameworks/methods leading to conceptually similar but formally distinct properties in different contexts. In this paper we provide a systematic analysis for this research landscape by making three main contributions. First, we identify groups of conceptually related properties in the literature, which can be regarded as based on common patterns and, using these patterns, we evidence that many further properties can be considered. Then, we provide a simplifying and unifying perspective for these properties by showing that they are all implied by the parametric principles of (either strict or non-strict) balance and monotonicity. Finally, we show that (instances of) these principles are satisfied by several quantitative argumentation formalisms in the literature, thus confirming their general validity and their utility to support a compact, yet comprehensive, analysis of properties of gradual argumentation.

FLAP Journal 2017 Journal Article

Editorial.

• Pietro Baroni
• Dov M. Gabbay
• Massimiliano Giacomin
• Leon van der Torre

KR Conference 2016 Conference Paper

Discontinuity-Free Decision Support with Quantitative Argumentation Debates

• Antonio Rago
• Francesca Toni
• Marco Aurisicchio
• Pietro Baroni

IBIS (Issue Based Information System) provides a widely adopted approach for knowledge representation especially suitable for the challenging task of representing wicked decision problems. While many tools for visualisation and collaborative development of IBIS graphs are available, automated decision support in this context is still underdeveloped, even though it would benefit several applications. QuAD (Quantitative Argumentation Debate) frameworks are a recently proposed IBIS-based formalism encompassing automated decision support by means of an algorithm for quantifying the strength of alternative decision options, based on aggregation of the strength of their attacking and supporting arguments. The initially proposed aggregation method, however, may give rise to discontinuities. In this paper we propose a novel, discontinuity-free algorithm for computing the strength of decision options in QuAD frameworks. We prove that this algorithm features several desirable properties and we compare the two aggregation methods, showing that both may be appropriate in the context of different application scenarios.

ECAI Conference 2016 Conference Paper

On Labelling Statements in Multi-Labelling Argumentation

• Pietro Baroni
• Guido Governatori
• Régis Riveret

In computational models of argumentation, argument justification has attracted more attention than statement justification, and significant sensitivity losses are identifiable when dealing with the justification of statements by otherwise appealing formalisms. This paper reappraises statement justification as a formalism-independent component in argument-based reasoning. We introduce a novel general model of argument-based reasoning based on multiple stages of labellings, the last one being devoted to statement justification, identify two alternative paths from argument acceptance to statement justification, and compare their expressiveness. We then show that this model encompasses several prominent literature proposals as special cases, thereby enabling a systematic comparison of existing approaches to statement justification, evidencing their merits and limits. Finally we illustrate our model by specifying a generic ignorance-aware statement justification and showing how it can be seamlessly integrated into different formalisms.

KR Conference 2016 Short Paper

On the Justification of Statements in Argumentation-based Reasoning

• Pietro Baroni
• Guido Governatori
• Ho-Pun Lam
• Regis Riveret

requirement for a knowledge representation and reasoning formalism. Surprisingly, the current versions of several well-known structured argumentation formalisms fail to satisfy this simple requirement, equating, for instance, the justification status of S4 with the one of S3, or with that of S1 and S2, or even the justification status of S3 with that of S1 and S2. While this may appear a severe drawback, we argue that this is not due to an intrinsic limitation of the argumentation formalisms themselves, rather to the relatively limited attention paid to the notion of justification of statements, often treated as a mere appendix of the notions of acceptance and justification of arguments, that (not surprisingly) are among the main focuses in formal argumentation studies. In order to overcome this limitation, we suggest that the issue of statement justification, in the context of argumentation-based reasoning, can be a subject of analysis on its own, where general, formalism-independent, principles and properties can be investigated, to be then applied uniformly across different specific formalisms. This paper makes some initial steps in this research direction by introducing a generic labelling-based model of argumentation-based reasoning process, where the notions of argument acceptance, argument justification, and statement justification are clearly distinguished and defined in a formalism-independent way, paving the way towards tunable statement justification. In the study of argumentation-based reasoning, argument justification has received far more attention than statement justification, often treated as a simple byproduct of the former. As a consequence, counterintuitive results and significant losses of sensitivity can be identified in the treatment of statement justification by otherwise appealing formalisms. To overcome this limitation, we propose to reappraise statement justification as a formalism-independent component. To this purpose, we introduce a novel general model of argumentationbased reasoning based on multiple levels of labellings, one of which is devoted to statement justification. This model is able to encompass several literature proposals as special cases: we illustrate this ability for the case of the ASPIC+ formalism and provide a first example of tunable statement justification in this context.

IJCAI Conference 2015 Conference Paper

Dealing with Generic Contrariness in Structured Argumentation

• Pietro Baroni
• Massimiliano Giacomin
• Beishui Liao

The adoption of a generic contrariness notion in ASPIC+ substantially enhances its expressiveness with respect to other formalisms for structured argumentation. In particular, it opens the way to novel investigation directions, like the use of multivalued logics in the construction of arguments. This paper points out however that in the current version of ASPIC+ a serious technical difficulty related with generic contrariness is present. With the aim of preserving the same level of generality, the paper provides a solution based on a novel notion of closure of the contrariness relation at the level of sets of formulas and an abstract representation of conflicts between sets of arguments. The proposed solution is shown to satisfy the same rationality postulates as ASPIC+ and represents a starting point for further technical and conceptual developments in structured argumentation.

AIJ Journal 2014 Journal Article

On the Input/Output behavior of argumentation frameworks

• Pietro Baroni
• Guido Boella
• Federico Cerutti
• Massimiliano Giacomin
• Leendert van der Torre
• Serena Villata

This paper tackles the fundamental questions arising when looking at argumentation frameworks as interacting components, characterized by an Input/Output behavior, rather than as isolated monolithical entities. This modeling stance arises naturally in some application contexts, like multi-agent systems, but, more importantly, has a crucial impact on several general application-independent issues, like argumentation dynamics, argument summarization and explanation, incremental computation, and inter-formalism translation. Pursuing this research direction, the paper introduces a general modeling approach and provides a comprehensive set of theoretical results putting the intuitive notion of Input/Output behavior of argumentation frameworks on a solid formal ground. This is achieved by combining three main ingredients. First, several novel notions are introduced at the representation level, notably those of argumentation framework with input, of argumentation multipole, and of replacement of multipoles within a traditional argumentation framework. Second, several relevant features of argumentation semantics are identified and formally characterized. In particular, the canonical local function provides an input-aware semantics characterization and a suite of decomposability properties are introduced, concerning the correspondences between semantics outcomes at global and local level. The third ingredient glues the former ones, as it consists of the investigation of some semantics-dependent properties of the newly introduced entities, namely S -equivalence of multipoles, S -legitimacy and S -safeness of replacements, and transparency of a semantics with respect to replacements. Altogether they provide the basis and draw the limits of sound interchangeability of multipoles within traditional frameworks. The paper develops an extensive analysis of all the concepts listed above, covering seven well-known literature semantics and taking into account various, more or less constrained, ways of partitioning an argumentation framework. Diverse examples, taken from the literature, are used to illustrate the application of the results obtained and, finally, an extensive discussion of the related literature is provided.

AIJ Journal 2014 Journal Article

On topology-related properties of abstract argumentation semantics. A correction and extension to Dynamics of argumentation systems: A division-based method

• Pietro Baroni
• Massimiliano Giacomin
• Beishui Liao

This research note provides novel results concerning the incremental computation of the stable and ideal argumentation semantics, by extending the division-based method presented in [1] and correcting a flawed claim given there. As a basis for these results, the note synthetically reviews and discusses the topology-related properties of directionality and SCC-recursiveness in abstract argumentation semantics and analyzes their relationships with the division-based method.

AIJ Journal 2013 Journal Article

Automata for infinite argumentation structures

• Pietro Baroni
• Federico Cerutti
• Paul E. Dunne
• Massimiliano Giacomin

The theory of abstract argumentation frameworks (afs) has, in the main, focused on finite structures, though there are many significant contexts where argumentation can be regarded as a process involving infinite objects. To address this limitation, in this paper we propose a novel approach for describing infinite afs using tools from formal language theory. In particular, the possibly infinite set of arguments is specified through the language recognized by a deterministic finite automaton while a suitable formalism, called attack expression, is introduced to describe the relation of attack between arguments. The proposed approach is shown to satisfy some desirable properties which cannot be achieved through other “naive” uses of formal languages. In particular, the approach is shown to be expressive enough to capture (besides any arbitrary finite structure) a large variety of infinite afs including two major examples from previous literature and two sample cases from the domains of multi-agent negotiation and ambient intelligence. On the computational side, we show that several decision and construction problems which are known to be polynomial time solvable in finite afs are decidable in the context of the proposed formalism and we provide the relevant algorithms. Moreover we obtain additional results concerning the case of finitary afs.

KER Journal 2011 Journal Article

An introduction to argumentation semantics

• Pietro Baroni
• Martin Caminada
• Massimiliano Giacomin

Abstract This paper presents an overview on the state of the art of semantics for abstract argumentation, covering both some of the most influential literature proposals and some general issues concerning semantics definition and evaluation. As to the former point, the paper reviews Dung's original notions of complete, grounded, preferred, and stable semantics, as well as subsequently proposed notions like semi-stable, ideal, stage, and CF2 semantics, considering both the extension-based and the labelling-based approaches with respect to their definitions. As to the latter point, the paper presents an extensive set of general properties for semantics evaluation and analyzes the notions of argument justification and skepticism. The final part of the paper is focused on the discussion of some relationships between semantics properties and domain-specific requirements.

IJCAI Conference 2009 Conference Paper

• Pietro Baroni
• Paul E. Dunne
• Massimiliano Giacomin

In the context of Dung’s theory of abstract argumentation frameworks, the recently introduced resolution-based grounded semantics features the unique property of fully complying with a set of general requirements, only partially satisfied by previous literature proposals. This paper contributes to the investigation of resolution-based grounded semantics by analyzing its computational properties with reference to a standard set of decision problems for abstract argumentation semantics: (a) checking the property of being an extension for a set of arguments; (b) checking agreement with traditional grounded semantics; (c) checking the existence of a non-empty extension; (d) checking credulous acceptance of an argument; (e) checking skeptical acceptance of an argument. It is shown that problems (a)-(c) admit polynomial time decision processes, while (d) is NP–complete and (e) coNP–complete.

AIJ Journal 2007 Journal Article

On principle-based evaluation of extension-based argumentation semantics

• Pietro Baroni
• Massimiliano Giacomin

The increasing variety of semantics proposed in the context of Dung's theory of argumentation makes more and more inadequate the example-based approach commonly adopted for evaluating and comparing different semantics. To fill this gap, this paper provides two main contributions. First, a set of general criteria for semantics evaluation is introduced by proposing a formal counterpart to several intuitive notions related to the concepts of maximality, defense, directionality, and skepticism. Then, the proposed criteria are applied in a systematic way to a representative set of argumentation semantics available in the literature, namely grounded, complete, preferred, stable, semi-stable, ideal, prudent, and CF2 semantics.

AIJ Journal 2005 Journal Article

SCC-recursiveness: a general schema for argumentation semantics

• Pietro Baroni
• Massimiliano Giacomin
• Giovanni Guida

In argumentation theory, Dung's abstract framework provides a unifying view of several alternative semantics based on the notion of extension. In this context, we propose a general recursive schema for argumentation semantics, based on decomposition along the strongly connected components of the argumentation framework. We introduce the fundamental notion of SCC-recursiveness and we show that all Dung's admissibility-based semantics are SCC-recursive, and therefore a special case of our schema. On these grounds, we argue that the concept of SCC-recursiveness plays a fundamental role in the study and definition of argumentation semantics. In particular, the space of SCC-recursive semantics provides an ideal basis for the investigation of new proposals: starting from the analysis of several examples where Dung's preferred semantics gives rise to questionable results, we introduce four novel SCC-recursive semantics, able to overcome the limitations of preferred semantics, while differing in other respects.

AIJ Journal 2005 Journal Article

Self-stabilizing defeat status computation: dealing with conflict management in multi-agent systems

• Pietro Baroni
• Massimiliano Giacomin
• Giovanni Guida

The role of argumentation in supporting various forms of interaction among possibly conflicting autonomous agents has been explicitly recognized in the literature. In argumentation, conflict management is carried out by the formal process of defeat status computation. In this paper we consider the generalization of this process to a distributed setting. We show that significant stabilization problems may arise even in relatively simple cases. A fundamental negative result is then proved: no general self-stabilizing algorithm exists for distributed defeat status computation, indicating that self-stabilizing algorithms for this problem can be defined only under specific conditions. Accordingly, we focus on two cases: an algorithm tailored to a specific family of inference graphs, that include only rebutting defeaters, and an algorithm that applies to any inference graph, also including undercutting defeaters, but may provide (cautiously) incorrect results for some nodes. For both algorithms the worst-case round complexity is analyzed and it is proved that no algorithms with lower complexity exist for the same tasks.

ECAI Conference 2004 Conference Paper

A General Recursive Schema for Argumentation Semantics

• Pietro Baroni
• Massimiliano Giacomin

NMR Workshop 2004 Conference Paper

A recursive approach to argumentation: motivation and perspectives

• Pietro Baroni
• Massimiliano Giacomin

In the context of Dung’s argumentation framework, we propose a general recursive schema for argumentation semantics, based on decomposition along the strongly connected components of the argumentation framework. We introduce the fundamental notion of SCCrecursiveness and show that all Dung’s admissibilitybased semantics are SCC-recursive, and therefore a special case of our schema. The space of SCC-recursive semantics provides a basis for the investigation of novel proposals: starting from the analysis of several examples where Dung’s preferred semantics gives rise to counterintuitive results, we introduce four novel SCCrecursive semantics, able to overcome the limitations of preferred semantics, while differing in other respects. Among them, the CF 2 semantics, which more radically departs from the traditional notion of admissibility, turns out to be the most satisfactory in all cases and, in particular, is able to correctly deal with the thorny problem of self-defeating arguments.

ECAI Conference 1998 Conference Paper

Diagnosis of Active Systems

• Pietro Baroni
• Gianfranco Lamperti
• Paolo Pogliano
• Marina Zanella