Pruning multi-extensions via exceptions

The main contribution of this paper is a method for pruning multi-extensions of a defeasible theory by using the exceptions to order the defeasible fonnulae. We construct a defeasible logic -- DEFEASIBLE WGIC WrrH EXCEFrIONS FIRST(DLEF) -- in which extensions are buílt taking into account the order on the defeasible fonnu1ae induced by the exceptions. This device prompts DLEF as a powerful tool to formalize common sense reasoning. It is on the formalization of the frame problem that we best evaluate the original features of DLEF. DLEF allows the formalization of the persistence axiom in the temporal projection problem in a stepwise way. That is, the persistence axiom is applied locally after every action is performed. Thus, if no exception to sorne properties is present while an action is performed the persistence axiom is used to conclude that those properties will remain unaltered in the resulting situation. Therefore, no property at the present is changed just for the sake of not changing sorne other properties in the future. The only reason for changes in properties are explicit changes provoked by the action being perfonned at the moment.Eje: 2do. Workshop sobre aspectos teóricos de la inteligencia artificialRed de Universidades con Carreras en Informática (RedUNCI

Computing Preferred Answer Sets by Meta-Interpretation in Answer Set Programming

Most recently, Answer Set Programming (ASP) is attracting interest as a new paradigm for problem solving. An important aspect which needs to be supported is the handling of preferences between rules, for which several approaches have been presented. In this paper, we consider the problem of implementing preference handling approaches by means of meta-interpreters in Answer Set Programming. In particular, we consider the preferred answer set approaches by Brewka and Eiter, by Delgrande, Schaub and Tompits, and by Wang, Zhou and Lin. We present suitable meta-interpreters for these semantics using DLV, which is an efficient engine for ASP. Moreover, we also present a meta-interpreter for the weakly preferred answer set approach by Brewka and Eiter, which uses the weak constraint feature of DLV as a tool for expressing and solving an underlying optimization problem. We also consider advanced meta-interpreters, which make use of graph-based characterizations and often allow for more efficient computations. Our approach shows the suitability of ASP in general and of DLV in particular for fast prototyping. This can be fruitfully exploited for experimenting with new languages and knowledge-representation formalisms.Comment: 34 pages, appeared as a Technical Report at KBS of the Vienna University of Technology, see http://www.kr.tuwien.ac.at/research/reports

Pruning multi-extensions via exceptions

The main contribution of this paper is a method for pruning multi-extensions of a defeasible theory by using the exceptions to order the defeasible fonnulae. We construct a defeasible logic -- DEFEASIBLE WGIC WrrH EXCEFrIONS FIRST(DLEF) -- in which extensions are buílt taking into account the order on the defeasible fonnu1ae induced by the exceptions. This device prompts DLEF as a powerful tool to formalize common sense reasoning. It is on the formalization of the frame problem that we best evaluate the original features of DLEF. DLEF allows the formalization of the persistence axiom in the temporal projection problem in a stepwise way. That is, the persistence axiom is applied locally after every action is performed. Thus, if no exception to sorne properties is present while an action is performed the persistence axiom is used to conclude that those properties will remain unaltered in the resulting situation. Therefore, no property at the present is changed just for the sake of not changing sorne other properties in the future. The only reason for changes in properties are explicit changes provoked by the action being perfonned at the moment.Eje: 2do. Workshop sobre aspectos teóricos de la inteligencia artificialRed de Universidades con Carreras en Informática (RedUNCI

First-order default logic revisited

Reiter’s original proposal for default logic is unsatisfactory for open default theories because of Skolemization and grounding. In this paper, we reconsider this long-standing problem and propose a new world view semantics for first-order default logic. Roughly speaking, a world view of a first-order default theory is a maximal collection of structures satisfying the default theory where the default part is fixed by the world view itself. We show how this semantics generalizes classical first-order logic and first-order answer set programming, and we discuss its connections to Reiter’s semantics and other related semantics. We also argue that first-order default logic under the world view semantics provides a rich framework for integrating classical logic based and rule based formalisms in the first-order case