Eric Würbel

Merging Belief Bases Represented by Logic Programs

This paper presents a method which allows for merging beliefs expressed thanks to logic programming with stable model semantics. This method is based on the syntactic merging operators described in the framework of propositional logic. The study of these operators leads to a new definition of the consequence relation between logic programs which is based on the logic of Here-and-There brought by Turner. Moreover, the specificity of the non-monotonic framework given by logic programming with stable model semantics allows for describing a weakened version of the merging operation. Once the operators are defined, their behaviour with respect to the Konieczny and Pino-Perez postulates for merging are examined and discussed.

Syntactic Propositional Belief Bases Fusion with Removed Sets

The problem of merging multiple sources information is central in several domains of computer science. In knowledge representation for artificial intelligence, several approaches have been proposed for propositional bases fusion, however, most of them are defined at a semantic level and are untractable. This paper proposes a new syntactic approach of belief bases fusion, called Removed Sets Fusion (RSF). The notion of removed-set, initially defined in the context of belief revision is extended to fusion and most of the classical fusion operations are syntactically captured by RSF. In order to efficiently implement RSF, the paper shows how RSF can be encoded into a logic program with answer set semantics, then presents an adaptation of the smodels system devoted to efficiently compute the removed sets in order to perform RSF. Finally a preliminary experimental study shows that the answer set programming approach seems promising for performing belief bases fusion on real scale applications.

Removed Set-Based Revision of Abstract Argumentation Frameworks

Argumentation frameworks have aroused intense interest from the AI community over the past years. Dynamic aspects of argumentation frameworks have received some interest from the community, but none of these works tries to address the recovering problem, that is, what shall we do when the new addition leads to the loss of all extensions. Such problem is typically a belief revision problem. In this paper, we propose a revision operator to revise an argumentation framework by another one, with the guarantee that the result of the operation will be an argumentation framework which has at least one stable extension. We also propose an algorithm to compute the revision operation outcome.

Underwater archaeological 3D surveys validation within the removed sets framework

This paper presents the results of the VENUS european project aimed at providing scientific methodologies and technological tools for the virtual exploration of deep water archaeological sites. We focused on underwater archaeological 3D surveys validation problem. This paper shows how the validation problem has been tackled within the Removed Sets framework, according to Removed Sets Fusion (RSF) and to the Partially Preordered Removed Sets Inconsistency Handling (PPRSIH). Both approaches have been implemented thanks to ASP and the good behaviour of the Removed Sets operations is presented through an experimental study on two underwater archaeological sites.

An Answer Set Programming Encoding of Prioritized Removed Sets Revision: Application to GIS

Geographical information systems are one of the most important application areas of belief revision. Recently, Wiirbel and colleagues [32] have applied the so-called removed sets revision (RSR) to the problem of assessment of water heights in a flooded valley. The application was partially satisfactory since only a small part of the valley has been handled. This paper goes one step further, and proposes an extension of (RSR) called Prioritized Removed Sets Revision (PRSR). We show that (PRSR) performed using answer set programming makes possible to solve a practical revision problem provided by a real application in the framework of geographical information system (GIS). We first show how PRSR can be encoded into a logic program with answer set semantics, we then present an adaptation of the smodels system devoted to efficiently compute the answer sets in order to perform PRSR. The experimental study shows that the answer set programming approach gives better results than previous implementations of RSR and in particular it allows to handle the whole valley. Lastly, some experimental studies comparing our encoding with implementations based on SAT-solvers are also provided.

Implementing Prioritized Merging with ASP

The paper addresses the extension of the removed sets framework to prioritized removed sets fusion (PRSF). It discusses the links between PRSF and iterated removed sets revision and shows that PRSF satisfy most of the postulates proposed for prioritized merging. An implementation of this new syntactic prioritized fusion operator is proposed thanks to answer sets programming.

Belief revision of GIS systems: the results of REV!GIS

This paper presents a synthesis of works performed on the practical tractability of revision on geographic information within the european REV!GIS project.It surveys di.erent representations of the revision problem as well as di.erent implementations of the adopted stategy: Removed Set Revision (RSR). A comparison of the representation formalisms is provided, a formal and an experimental comparison is conducted on the various implementations on real scale applications in the context of GIS.

An anytime revision operator for large and uncertain geographic data sets

Abstract The environmental data are in general imprecise and uncertain, but they are located in space and therefore obey to spatial constraints. The “spatial analysis” is a (natural) reasoning process through which geographers take advantage of these constraints to reduce this uncertainty and to improve their beliefs. Trying to automate this process is a really hard problem. We propose here the design of a revision operator able to perform a spatial analysis in the context of one particular “application profile”: it identifies objects bearing a same variable bound through local constraints. The formal background, on which this operator is built, is a decision algorithm from Reiter [9]; then the heuristics, which help this algorithm to become tractable on a true scale application, are special patterns for clauses and “spatial confinement” of conflicts. This operator is “anytime”, because it uses “samples” and works on small (tractable) blocks, it reaggregates the partial revision results on larger blocks, thus we name it a “hierarchical block revision” operator. Finally we illustrate a particular application: a flooding propagation. Of course this is among possible approaches of “soft-computing” for geographic applications.

Possibilistic ASP Base Revision by Certain Input

Belief base revision has been studied within the answer set programming framework. We go a step further by introducing uncertainty and studying belief base revision when beliefs are represented by possibilistic logic programs under possibilistic answer set semantics and revised by certain input. The paper proposes two approaches of rule-based revision operators and presents their semantic characterization in terms of possibilistic distribution. This semantic characterization allows for equivalently considering the evolution of syntactic logic programs and the evolution of their semantic content. It then studies the logical properties of the proposed operators and gives complexity results.

A Semantic Characterization for ASP Base Revision

The paper deals with base revision for Answer Set Programming (ASP). Base revision in classical logic is done by the removal of formulas. Exploiting the non-monotonicity of ASP allows one to propose other revision strategies, namely addition strategy or removal and/or addition strategy. These strategies allow one to define families of rule-based revision operators. The paper presents a semantic characterization of these families of revision operators in terms of answer sets. This characterization allows one to equivalently consider the evolution of syntactic logic programs and the evolution of their semantic content.