Giovanni Guida

SCC-recursiveness: a general schema for argumentation semantics

In argumentation theory, Dungs 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 Dungs 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 Dungs 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.

NLI: a robust interface for natural language person-machine communication

Abstract In this paper, a novel approach to natural language understanding, called goal oriented parsing, is presented. Such a model of comprehension is embedded in the more general frame of interpersonal communication and is applied to the person-machine interaction task. It is based on the claim that understanding imperative natural language is strongly dependent both on the goal of the speaker and on the nature of the hearer. This assumption has proved appropriate for the design of effective and robust natural language interfaces to artificial systems. This approach is supported by the development of an experimental project, called NLI, for enquiring in Italian a relational data base. NLI is to date running on a PDP 11/34 computer at the University of Udine. In this paper we illustrate the overall architecture of the system, along with the basic features of the parsing algorithm. This is based on the new concept of hierarchical parsing and is mainly directed by the semantics of the language. The role of clarification dialogue to overcome critical situations is discussed as well. The use of goal oriented parsing in dealing with full query text and anaphora is also exploited. Several meaningful examples are presented. Comparisons with related works are outlined and promising directions deserving further investigation are presented.

AFRA: Argumentation framework with recursive attacks

The issue of representing attacks to attacks in argumentation is receiving an increasing attention as a useful conceptual modelling tool in several contexts. In this paper we present AFRA, a formalism encompassing unlimited recursive attacks within argumentation frameworks. AFRA satisfies the basic requirements of definition simplicity and rigorous compatibility with Dungs theory of argumentation. This paper provides a complete development of the AFRA formalism complemented by illustrative examples and a detailed comparison with other recursive attack formalizations.

Encompassing Attacks to Attacks in Abstract Argumentation Frameworks

In the traditional definition of Dungs abstract argumentation framework (

Forward and backward reasoning in automatic abstracting

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Brief paper: An expert intermediary system for interactive document retrieval

), the notion of attack is understood as a relation between arguments, thus bounding attacks to start from and be directed to arguments. This paper introduces a generalized definition of abstract argumentation framework called

A distributed multi-agent architecture for natural language processing

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The Active Layer

(Argumentation Framework with Recursive Attacks), where an attack is allowed to be directed towards another attack. From a conceptual point of view, we claim that this generalization supports a straightforward representation of reasoning situations which are not easily accommodated within the traditional framework. From the technical side, we first investigate the extension to the generalized framework of the basic notions of conflict-free set, acceptable argument, admissible set and of Dungs fundamental lemma. Then we propose a correspondence from the

Building Expert Systems: From Life Cycle to Development Methodology

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IR-NLI II: applying man-machine interaction and artificial intelligence conceptsto information retrieval

to the