Valentina Gliozzi

Labels as Features (Not Names) for Infant Categorization: A Neurocomputational Approach

A substantial body of experimental evidence has demonstrated that labels have an impact on infant categorization processes. Yet little is known regarding the nature of the mechanisms by which this effect is achieved. We distinguish between two competing accounts: supervised name-based categorization and unsupervised feature-based categorization. We describe a neurocomputational model of infant visual categorization, based on self-organizing maps, that implements the unsupervised feature-based approach. The model successfully reproduces experiments demonstrating the impact of labeling on infant visual categorization reported in Plunkett, Hu, and Cohen (2008). It mimics infant behavior in both the familiarization and testing phases of the procedure, using a training regime that involves only single presentations of each stimulus and using just 24 participant networks per experiment. The model predicts that the observed behavior in infants is due to a transient form of learning that might lead to the emergence of hierarchically organized categorical structure and that the impact of labels on categorization is influenced by the perceived similarity and the sequence in which the objects are presented. The results suggest that early in development, say before 12 months old, labels need not act as invitations to form categories nor highlight the commonalities between objects, but they may play a more mundane but nevertheless powerful role as additional features that are processed in the same fashion as other features that characterize objects and object categories.

Semantic characterization of rational closure: From propositional logic to description logics

Abstract In this paper we provide a semantic reconstruction of rational closure. We first consider rational closure as defined by Lehman and Magidor [33] for propositional logic, and we provide a semantic characterization based on a minimal models mechanism on rational models. Then we extend the whole formalism and semantics to Description Logics, by focusing our attention to the standard ALC : we first naturally adapt to Description Logics Lehman and Magidors propositional rational closure, starting from an extension of ALC with a typicality operator T that selects the most typical instances of a concept C (hence T ( C ) stands for typical C). Then, for the Description Logics, we define a minimal model semantics for the logic ALC and we show that it provides a semantic characterization for the rational closure of a Knowledge base. We consider both the rational closure of the TBox and the rational closure of the ABox.

Verifying business process compliance by reasoning about actions

In this paper we address the problem of verifying business process compliance with norms. To this end, we employ reasoning about actions in a temporal action theory. The action theory is defined through a combination of Answer Set Programming and Dynamic Linear Time Temporal Logic (DLTL). The temporal action theory allows us to formalize a business process as a temporal domain description, possibly including temporal constraints. Obligations in norms are captured by the notion of commitment, which is borrowed from the social approach to agent communication. Norms are represented using (possibly) non monotonic causal laws which (possibly) enforce new obligations. In this context, verifying compliance amounts to verify that no execution of the business process leaves some commitment unfulfilled. Compliance verification can be performed by Bounded Model Checking.

Analytic tableaux calculi for KLM logics of nonmonotonic reasoning

We present tableau calculi for the logics of nonmonotonic reasoning defined by Kraus, Lehmann and Magidor (KLM). We give a tableau proof procedure for all KLM logics, namely preferential, loop-cumulative, cumulative, and rational logics. Our calculi are obtained by introducing suitable modalities to interpret conditional assertions. We provide a decision procedure for the logics considered and we study their complexity.

Weak AGM postulates and strong Ramsey Test: A logical formalization

We reformulate AGM postulates for belief revision systems that may contain conditional formulas. We show that we can establish a mapping between belief revision systems and conditionals by means of the so called Ramsey Test, without incurring Gardenfors triviality result. We then derive the conditional logic BCR from our revision postulates by means of a strong version of the Ramsey Test. We give a sound and complete axiomatization of this logic with respect to its standard selection-function models semantics, and we prove its decidability. We finally show that there is an isomorphism between belief revision systems and selection function models of BCR via a representation theorem. The logic BCR provides a logical formalization of belief revision in the language of conditional logic.

Preferential vs Rational Description Logics: which one for Reasoning About Typicality?

Extensions of Description Logics (DLs) to reason about typicality and defeasible inheritance have been largely investigated. In this paper, we consider two such extensions, namely (i) the extension of DLs with a typicality operator T, having the properties of Preferential nonmonotonic entailment P, and (ii) its variant with a typicality operator having the properties of the stronger Rational entailment R. The first one has been proposed in [6]. Here, we investigate the second one and we show, by a representation theorem, that it is equivalent to the approach to preferential subsumption proposed in [3]. We compare the two extensions, preferential and rational, and argue that the first one is more suitable than the second one to reason about typicality, as the latter leads to very unintuitive inferences.

A minimal model semantics for nonmonotonic reasoning

This paper provides a general semantic framework for nonmonotonic reasoning, based on a minimal models semantics on the top of KLM systems for nonmonotonic reasoning. This general framework can be instantiated in order to provide a semantic reconstruction within modal logic of the notion of rational closure, introduced by Lehmann and Magidor. We give two characterizations of rational closure: the first one in terms of minimal models where propositional interpretations associated to worlds are fixed along minimization, the second one where they are allowed to vary. In both cases a knowledge base must be expanded with a suitable set of consistency assumptions, represented by negated conditionals. The correspondence between rational closure and minimal model semantics suggests the possibility of defining variants of rational closure by changing either the underlying modal logic or the comparison relation on models.

Analytic tableaux for KLM preferential and cumulative logics

We present tableau calculi for some logics of default reasoning, as defined by Kraus, Lehmann and Magidor. We give a tableau proof procedure for preferential and cumulative logics. Our calculi are obtained by introducing suitable modalities to interpret conditional assertions. Moreover, they give a decision procedure for the respective logics and can be used to establish their complexity.

Tableau calculus for preference-based conditional logics: PCL and its extensions

We present a tableau calculus for some fundamental systems of propositional conditional logics. We consider the conditional logics that can be characterized by preferential semantics (i.e., possible world structures equipped with a family of preference relations). For these logics, we provide a uniform completeness proof of the axiomatization with respect to the semantics, and a uniform labeled tableau procedure.

Tableau Calculi for Preference-Based Conditional Logics

In this paper we develop labelled and uniform tableau methods for some fundamental system of propositional conditional logics. We consider the well-known system CE (that can be seen as a generalization of preferential nonmonotonic logic), and some related systems. Our tableau proof procedures are based on a possible-worlds structures endowed with a family of preference relations. The tableau procedure gives the first practical decision procedure for CE.