8,992 research outputs found
Abduction and Dialogical Proof in Argumentation and Logic Programming
We develop a model of abduction in abstract argumentation, where changes to
an argumentation framework act as hypotheses to explain the support of an
observation. We present dialogical proof theories for the main decision
problems (i.e., finding hypothe- ses that explain skeptical/credulous support)
and we show that our model can be instantiated on the basis of abductive logic
programs.Comment: Appears in the Proceedings of the 15th International Workshop on
Non-Monotonic Reasoning (NMR 2014
Well-Founded Semantics for Extended Datalog and Ontological Reasoning
The Datalog± family of expressive extensions of Datalog has recently been introduced as a new paradigm for query answering over ontologies, which captures and extends several common description logics. It extends plain Datalog by features such as existentially quantified rule heads and, at the same time, restricts the rule syntax so as to achieve decidability and tractability. In this paper, we continue the research on Datalog±. More precisely, we generalize the well-founded semantics (WFS), as the standard semantics for nonmonotonic normal programs in the database context, to Datalog± programs with negation under the unique name assumption (UNA). We prove that for guarded Datalog± with negation under the standard WFS, answering normal Boolean conjunctive queries is decidable, and we provide precise complexity results for this problem, namely, in particular, completeness for PTIME (resp., 2-EXPTIME) in the data (resp., combined) complexity
Revision based total semantics for extended normal logic programs
Dissertação para obtenção do Grau de Doutor em
Matemática - Lógica e Fundamentos da MatemáticaFundação para a Ciência e Tecnologia - SFRH/ PROTEC/49747/200
Every normal logic program has a 2-valued semantics: theory, extensions, applications, implementations
Trabalho apresentado no âmbito do Doutoramento em Informática, como requisito parcial para obtenção do grau de Doutor em InformáticaAfter a very brief introduction to the general subject of Knowledge Representation and Reasoning with Logic Programs we analyse the syntactic structure of a logic program and how it can influence the semantics. We outline the important properties of a 2-valued semantics for Normal Logic Programs, proceed to define the new Minimal Hypotheses semantics with those properties and explore how it can be used to benefit some knowledge representation and reasoning mechanisms.
The main original contributions of this work, whose connections will be detailed in
the sequel, are:
• The Layering for generic graphs which we then apply to NLPs yielding the Rule
Layering and Atom Layering — a generalization of the stratification notion;
• The Full shifting transformation of Disjunctive Logic Programs into (highly nonstratified)NLPs;
• The Layer Support — a generalization of the classical notion of support;
• The Brave Relevance and Brave Cautious Monotony properties of a 2-valued semantics;
• The notions of Relevant Partial Knowledge Answer to a Query and Locally Consistent
Relevant Partial Knowledge Answer to a Query;
• The Layer-Decomposable Semantics family — the family of semantics that reflect
the above mentioned Layerings;
• The Approved Models argumentation approach to semantics;
• The Minimal Hypotheses 2-valued semantics for NLP — a member of the Layer-Decomposable Semantics family rooted on a minimization of positive hypotheses assumption approach;
• The definition and implementation of the Answer Completion mechanism in XSB
Prolog — an essential component to ensure XSB’s WAM full compliance with the
Well-Founded Semantics;
• The definition of the Inspection Points mechanism for Abductive Logic Programs;• An implementation of the Inspection Points workings within the Abdual system [21]
We recommend reading the chapters in this thesis in the sequence they appear. However,
if the reader is not interested in all the subjects, or is more keen on some topics
rather than others, we provide alternative reading paths as shown below.
1-2-3-4-5-6-7-8-9-12 Definition of the Layer-Decomposable Semantics family and the Minimal Hypotheses semantics (1 and 2 are optional)
3-6-7-8-10-11-12 All main contributions – assumes the reader
is familiarized with logic programming topics
3-4-5-10-11-12 Focus on abductive reasoning and applications.FCT-MCTES (Fundação para a Ciência e Tecnologia do Ministério da Ciência,Tecnologia e Ensino Superior)- (no. SFRH/BD/28761/2006
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
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