Hypothetical reasoning with well founded semantics

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Adding closed world assumptions to well-founded semantics

Given a program P we specify an enlargement of its well-founded model which gives meaning to the adding of closed world assumptions. We do so by proposing the desirable principles of a closed world assumption (CWA), and proceed to formally define and apply them to well-founded semantics (WFS), in order to obtain a WFS added with CWA, the O-semantics. After an introduction and motivating examples, there follow the presentation of the concepts required to formalize the model structure, the properties it enjoys, and the criteria and procedures which follow the precise characterization of the preferred unique maximal model that gives the intended meaning to the O-semantics of a program, the O-model. Some properties are also exhibited that permit a more expedite obtention of the models. Several detailed examples are introduced throughout to illustrate the concepts and their application. Comparison is made with other work, and in the conclusions the novelty of the approach is brought out.authorsversionpublishe

Contradiction removal within well founded semantics

Our purpose is to define a semantics that extends Well Founded Semantics for programs with classical negation, and which avoids the absence of models caused by contradictions brought about by closed world assumptions. This extension relies on allowing to take back such closed world assumptions, through making their truth value become undefined, and thus permiting noncontradictory models to appear. We take back such assumptions in a minimal way for all alternative ways of removing contradictions, by means of simple transformations of the original program. The transformed programs have contradiction free Well Founded Models. Moreover, we identify a unique model that defines the semantics of the original program, which is included in all the alternative contradiction free models. This unique model coincides with the Well Founded Model when the latter is noncontradictory. The notions of minimality and contradiction removal employed are useful for dealing with Belief Revision. These techniques for removing contradiction in the sense of integrity constraints violation. Another important result is that our removal semantics (the contradiction removal semantivs) is defined as the Well Founded Model of a derived program obtained by simple transformation from the original one. Thus no new model determining algorithms are needed. For noncontradictory programs the two programs coincide.authorsversionpublishe

Nonmonotonic reasoning with well founded semantics

Well Founded Semantics is adequate to capture nonmonotonic reasoning if we interpret the Well Founded model of a program P as a (possibly incomplete) view of the world. Thus the Well Founded model may be accepted to be a definite view of the world and the extended stable models as alternative enlarged consistent belief models an agent may have about the world. Our purpose is to exhibit a modular systematic method of representing nonmonotonic problems with the Well Founded semantics of logic programs. In this paper we use this method to represent and solve some classical nonmonotonic problems. This leads us to consider our method quite generic.publishersversionpublishe

SLX - A TOP-DOWN DERIVATION PROCEDURE FOR PROGRAMS WITH EXPLICIT NEGATION

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Diagnosis and debugging as contradiction removal

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Dynamic Logic Programming

In this paper we investigate updates of knowledge bases represented by logic programs. In order to represent negative information, we use generalized logic programs which allow default negation not only in rule bodies but also in their heads.We start by introducing the notion of an update P U of a logic program P by another logic program U. Subsequently, we provide a precise semantic characterization of P U, and study some basic properties of program updates. In particular, we show that our update programs generalize the notion of interpretation update. We then extend this notion to compositional sequences of logic programs updates P1P2 ::: , dening a dynamic program update, and thereby introducing the paradigm of dynamic logic programming. This paradigm significantly facilitates modularization of logic programming, and thus modularization of nonmonotonic reasoning as a whole. Specically, suppose that we are given a set of logic program modules, each describing a dierent state of our knowledge of the world. Dierent states may represent dierent time points or dierent sets of priorities or perhaps even dierent viewpoints. Consequently, program modules may contain mutually contradictory as well as overlapping information. The role of the dynamic program update is to employ the mutual relationships existing between dierent modules to precisely determine, at any given module composition stage, the declarative as well as the procedural semantics of the combined program resulting from the modules.authorsversionpublishe

Realisation of Stepping for Real-World ASP Languages

perpétuo e sem limites geográficos, de arquivar e publicar esta dissertação através de exemplares impressos reproduzidos em papel ou de forma digital, ou por qualquer outro meio conhecido ou que venha a ser inventado, e de a divulgar através de repositórios científicos e de admitir a sua cópia e distribuição com objectivos educacionais ou de investigação, não comerciais, desde que seja dado crédito ao autor e editor. ivFor MelisviAcknowledgements I would like to thank my supervisor for having a lot of patience with me, the team at TUW for having this wonderful idea, Melis and Ingo for support, and my family, this would not be possible without them. Stepping is folklore in debugging of procedural programming languages that allows developers to focus their attention to each statement of their program one after the other. Recent results in the field of answer-set programming (ASP) debugging brought forth a formalism for stepping through answer-set programs. The main idea is to monotonically build up an interpretation by, at each step, adding literals derived by a rule that is active under the partial interpretation obtained in the previous step. As the stepping framewor

Automated reasoning on the web

Automated reasoning is becoming an essential issue in many Web systems and applications, especially in emerging Semantic Web applications. This article first discusses reasons for this evolution. Then, it presents research issues currently investigated towards automated reasoning on the Web and it introduces into selected applications demonstrating the practical impact of the approach. Finally, it introduces a research endeavor called REWERSE (cf