Knowledge Compilation of Logic Programs Using Approximation Fixpoint Theory

To appear in Theory and Practice of Logic Programming (TPLP), Proceedings of ICLP 2015 Recent advances in knowledge compilation introduced techniques to compile \emph{positive} logic programs into propositional logic, essentially exploiting the constructive nature of the least fixpoint computation. This approach has several advantages over existing approaches: it maintains logical equivalence, does not require (expensive) loop-breaking preprocessing or the introduction of auxiliary variables, and significantly outperforms existing algorithms. Unfortunately, this technique is limited to \emph{negation-free} programs. In this paper, we show how to extend it to general logic programs under the well-founded semantics. We develop our work in approximation fixpoint theory, an algebraical framework that unifies semantics of different logics. As such, our algebraical results are also applicable to autoepistemic logic, default logic and abstract dialectical frameworks

Introduction to the 28th International Conference on Logic Programming Special Issue

We are proud to introduce this special issue of the Journal of Theory and Practice of Logic Programming (TPLP), dedicated to the full papers accepted for the 28th International Conference on Logic Programming (ICLP). The ICLP meetings started in Marseille in 1982 and since then constitute the main venue for presenting and discussing work in the area of logic programming

Stable Model Counting and Its Application in Probabilistic Logic Programming

Model counting is the problem of computing the number of models that satisfy a given propositional theory. It has recently been applied to solving inference tasks in probabilistic logic programming, where the goal is to compute the probability of given queries being true provided a set of mutually independent random variables, a model (a logic program) and some evidence. The core of solving this inference task involves translating the logic program to a propositional theory and using a model counter. In this paper, we show that for some problems that involve inductive definitions like reachability in a graph, the translation of logic programs to SAT can be expensive for the purpose of solving inference tasks. For such problems, direct implementation of stable model semantics allows for more efficient solving. We present two implementation techniques, based on unfounded set detection, that extend a propositional model counter to a stable model counter. Our experiments show that for particular problems, our approach can outperform a state-of-the-art probabilistic logic programming solver by several orders of magnitude in terms of running time and space requirements, and can solve instances of significantly larger sizes on which the current solver runs out of time or memory.Comment: Accepted in AAAI, 201

An overview of the ciao multiparadigm language and program development environment and its design philosophy

We describe some of the novel aspects and motivations behind the design and implementation of the Ciao multiparadigm programming system. An important aspect of Ciao is that it provides the programmer with a large number of useful features from different programming paradigms and styles, and that the use of each of these features can be turned on and off at will for each program module. Thus, a given module may be using e.g. higher order functions and constraints, while another module may be using objects, predicates, and concurrency. Furthermore, the language is designed to be extensible in a simple and modular way. Another important aspect of Ciao is its programming environment, which provides a powerful preprocessor (with an associated assertion language) capable of statically finding non-trivial bugs, verifying that programs comply with specifications, and performing many types of program optimizations. Such optimizations produce code that is highly competitive with other dynamic languages or, when the highest levéis of optimization are used, even that of static languages, all while retaining the interactive development environment of a dynamic language. The environment also includes a powerful auto-documenter. The paper provides an informal overview of the language and program development environment. It aims at illustrating the design philosophy rather than at being exhaustive, which would be impossible in the format of a paper, pointing instead to the existing literature on the system

A Search for the Optical Counterpart of the Luminous X-ray Source in NGC 6652

We examine images of the field of X1832-330, the luminous (Lx ~ 10^36 erg/s) X-ray burst source near the center of the globular cluster NGC 6652, in order to identify the optical counterpart for further study. U and B ground-based images allow us to set a limit M_B > 3.5 for the counterpart at the time of those observations, provided that the color is (U-B)_0 ~ -1, similar to the sources known in other clusters. Archival Hubble Space Telescope observations survey most but not all of the 1 sigma X-ray error circle, and allow us to set limits M_B > 5.9 and M_B > 5.2 in the WF/PC and WFPC2 regions, respectively. In the WF/PC images we do weakly detect a faint object with UV-excess, but it is located 11.7'' from the ROSAT X-ray position. This considerable (2.3 sigma) discrepancy in position suggests that this candidate be treated with caution, but it remains the only reasonable one advanced thus far. We measure for this star m_439 = 20.2 +- 0.2, (m_336 - m_439) = -0.5 +- 0.2, and estimate M_B = 5.5, (U-B)_0 = -0.9, similar to other known optical counterparts. If this candidate is not the identification, our limits imply that the true counterpart, not yet identified, is probably the optically-faintest cluster source yet known, or alternatively that it did not show significant UV excess at the time of these observations. Finally, we assess the outlook for the identification of the remaining luminous globular cluster X-ray sources.Comment: 15 pages including 5 figures and no tables. Accepted for publication in The Astronomical Journal; to appear in Volume 116, September 1998. A preprint with full resolution figures may be downloaded from http://www.astro.washington.edu/deutsch/pubs