Semantics of logic programs with explicit negation

After a historical introduction, the bulk of the thesis concerns the study of a declarative semantics for logic programs. The main original contributions are: ² WFSX (Well–Founded Semantics with eXplicit negation), a new semantics for logic programs with explicit negation (i.e. extended logic programs), which compares favourably in its properties with other extant semantics. ² A generic characterization schema that facilitates comparisons among a diversity of semantics of extended logic programs, including WFSX. ² An autoepistemic and a default logic corresponding to WFSX, which solve existing problems of the classical approaches to autoepistemic and default logics, and clarify the meaning of explicit negation in logic programs. ² A framework for defining a spectrum of semantics of extended logic programs based on the abduction of negative hypotheses. This framework allows for the characterization of different levels of scepticism/credulity, consensuality, and argumentation. One of the semantics of abduction coincides with WFSX. ² O–semantics, a semantics that uniquely adds more CWA hypotheses to WFSX. The techniques used for doing so are applicable as well to the well–founded semantics of normal logic programs. ² By introducing explicit negation into logic programs contradiction may appear. I present two approaches for dealing with contradiction, and show their equivalence. One of the approaches consists in avoiding contradiction, and is based on restrictions in the adoption of abductive hypotheses. The other approach consists in removing contradiction, and is based in a transformation of contradictory programs into noncontradictory ones, guided by the reasons for contradiction.

Segurança e criminalidade organizada

Globalization brought some deep changes to the world (dis)order. Nowadays, more than in other moment in history, we are closer to the ones physically far, living in “global village” called by Marshall McLuhan (1962). The concepts and premises built in this new order, have totally broken with the ones that “came out from Westphalia”, which had last to the end of the cold war, like, for example, the concept of security. Since then, security has been facing one of its biggest transformations ever, completely disrupting the state border based idea and starting to be extended to other domains, as human, economic, environmental and IT security, among others. In this global and interdependent environment, “new” threats and risks have raised, which are demanding a comprehensive approach from the States, international organizations and other actors, to allow the analysis and understanding its impacts on the various society sectors and orders. Inside the enormous challenges to the global security, it is important to regard the organized crime, which covers, by itself, a set of threats and risks, enhanced by its connection to other types of criminality, such as terrorism. The goals pursued and the tactics used by criminal organizations during the perpetration of illegal activities, specially the drug smuggling, have impact in an wide spectrum of the social, economic financial and politic dimensions, which should not be underestimated, otherwise our own security may be compromised. Therefore, the current investigation intends to be an important catalyst to the idea debate inside security scope, through the analysis of the organized crime and the drug smuggling, adding to a discussion of this issue, which should be deeper and holistic, aiming a better understanding of the challenges provided by our society.