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.

Asking why

The growth of a solid, knowledge-intensive firm, OutSystems—an IT company recognized in 2003 by Fortune magazine as one of the most promising start-ups in the world—is accompanied by efforts to create a strong culture that preserves the traits that have driven OutSystems’ success and that drives innovation, adaptability, high performance, and accountability. The lessons OutSystems learned from previous international experiences are presented along with its latest growth model of branded local partners. The case study is intended to introduce concepts related to organizational culture, traits of cultures that drive innovation, national versus organizational culture, and the challenges of globalization. It is designed to be used in Organizational Behavior classes and is appropriate for MBA- and Master’s-level courses in the area of management. It is suggested as a guideline for 60- to 90-minute classes. Participants are invited to discuss the importance of organizational cultures and their fit with the company strategy. Participants are also encouraged to brainstorm about the best approach to face OutSystems’ new stage of growth, specifically the advantages and consequences of growing as a metanational company. Finally, in the conclusion, the most relevant findings taken from the discussions proposed are revisited: The importance of an organizational culture adapted to the market needs and the potential of innovation behind metanational companies. Other considerations are made about: how the case illustrates the importance of leadership, group age, and group size in the process of building a culture; and how OutSystems’ culture solves the apparent contradiction behind adaptable culture.