Local Closed-World Reasoning with Description Logics under the Well-Founded Semantics

An important question for the upcoming Semantic Web is how to best combine open world ontology languages, such as the OWL-based ones, with closed world rule-based languages. One of the most mature proposals for this combination is known as hybrid MKNF knowledge bases (Motik and Rosati, 2010 [52]), and it is based on an adaptation of the Stable Model Semantics to knowledge bases consisting of ontology axioms and rules. In this paper we propose a well-founded semantics for nondisjunctive hybrid MKNF knowledge bases that promises to provide better efficiency of reasoning, and that is compatible with both the OWL-based semantics and the traditional Well-Founded Semantics for logic programs. Moreover, our proposal allows for the detection of inconsistencies, possibly occurring in tightly integrated ontology axioms and rules, with only little additional effort. We also identify tractable fragments of the resulting language

A semantica dos programas logicos com negacao explicita

After a historical introduction, the bulk of the thesis concerns the study of a declarative semantics for logic programs. The main original contributions are: 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. A generic characterization schema that facilitates comparisons among a diversity of semantics of extended logic programs, including WFSX. 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. 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. 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. 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 show their equivalence. One of the approaches consists in avoiding contradiction, and is based on restrictions in the adoption of adductive hypotheses. The other approach consists in removing contradiction, and is based in a transformation of contradictory programs into non contradictory ones, guided by the reasons for contradictionAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1249-074 Lisboa, Portugal / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga

Semantica de programas logicos com negacao explicita

After historical introduction, the bulk of the thesis concerns the study of a declarative semantics for logic programs. The main original contributions are: . WFSX (Well-Founded Semantics with explicit negation), a new semantics for logic programs with explicit negation (i.e. extended logic program); which compares favorably in its properties with other extant semantics. . A generic characterization schema that facilitates comparisons among a diversity of semantics of extended logic programs, including WFSX. . 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. . 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 skepticism/credulity, consensuality, and argumentation. . O-semantics, a semantics that adds more CWA hypotheses to WFSX. The techniques used for doing so also applicable to the well founded semantics of normal programs. . By introducing explicit negation into a logic programs contradiction may appear. I present two approaches for dealing with contradiction, and show their equivalence. One of the approaches 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 non contradictory ones, guided by the reasons for contradictionAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga

Reasoning with Logic Programming

ew with pointers to main references, it reviews and compares the main approaches in the field to our own, and it contains all proofs and basic definitions, though the interest reader will want to consult, e.g., [200, 201, 172, 131, 16], for more extensive overviews of its subject matter and surrounding areas. It shows a variety of applications that illustrate the use, wide scope, and potential of logic programming for performing various types of reasoning, We are honoured to have been awarded in 1995 for this book "Premio Boa Esperanca", the highest science prize from the Portuguese government. VI namely non-monotonic ones such as: dealing with incomplete information; default, hypothetical and counterfactual reasoning; contradiction handling; belief revision; and abduction. And it shows a variety of knowledge representation forms such as: falsity, both via explicit negation and (implicit) default negation (or by failure); constraints (denials); default rules; exceptions to defaul

A Coherent Well-founded Model for Hybrid MKNF Knowledge Bases

With the advent of the Semantic Web, the question becomes important how to best combine open-world based ontology languages, like OWL, with closed-world rules paradigms. One of the most mature proposals for this combination is known as Hybrid MKNF knowledge bases [11], which is based on an adaptation of the stable model semantics to knowledge bases consisting of ontology axioms and rules. In this paper, we propose a well-founded semantics for such knowledge bases which promises to provide better efficiency of reasoning, which is compatible both with the OWL-based semantics and the traditional well-founded semantics for logic programs, and which surpasses previous proposals for such a well-founded semantics by avoiding some issues related to inconsistency handling

Vivid Agents Arguing about Distributed Extended Logic Programs

Argumentation semantics in extended logic programming has been defined in [5,12] for a single agent which determines its believes by an internal argumentation process. In this paper we extend the initial argumentation framework to a multi-agent setting including both argumentation and cooperation. We define inference for multi-agent systems and define an algorithm for inference. We sketch an argumentation protocol and line out by an example how it is implemented using vivid agents [15,13]. Keywords: Multi-Agent Systems, Argumentation, Logic Programming

Top-Down Query Evaluation for Well-Founded Semantics With Explicit Negation

In this paper we define a sound and complete top--down semantic tree characterization, that includes pruning rules, of the well--founded semantics for programs extended with explicit negation (WFSX), and compare it to other related approaches. It is amenable to a simple implementation (in appendix), and by its nature readily allows pre--processing into Prolog, showing promise as an efficient basis for further development. Because of its properties, which other competing semantics do not fully enjoy, WFSX is a natural candidate to being the semantics of choice for extended logic programs. Namely, it exhibits the structural properties: simplicity, cumulativity, rationality, relevance, partial evaluation, and polynomial complexity for DATALOG. It provides a qualitative representational expressivity that can capture a wide variety of logical reasoning forms, and serve as an instrument for programming them. Since WFSX coincides with the well--founded semantics on normal programs, our method..

Evolving Logic Programs

Logic programming has often been considered less than adequate for modelling the dynamics of knowledge changing over time