Marcelo Finger

Adding a temporal dimension to a logic system

We introduce a methodology whereby an arbitrary logic system L can be enriched with temporal features to create a new system T(L). The new system is constructed by combining L with a pure propositional temporal logic T (such as linear temporal logic with “Since” and “Until”) in a special way. We refer to this method as “adding a temporal dimension to L” or just “temporalising L”. We show that the logic system T(L) preserves several properties of the original temporal logic like soundness, completeness, decidability, conservativeness and separation over linear flows of time. We then focus on the temporalisation of first-order logic, and a comparison is make with other first-order approaches to the handling of time.

InteGrade: object‐oriented Grid middleware leveraging the idle computing power of desktop machines

Grid computing technology improves the computing experiences at organizations by effectively integrating distributed computing resources. However, just a small fraction of currently available Grid infrastructures focuses on reutilization of existing commodity computing resources. This paper introduces InteGrade, a novel object‐oriented middleware Grid infrastructure that focuses on leveraging the idle computing power of shared desktop machines. Its features include support for a wide range of parallel applications and mechanisms to assure that the owners of shared resources do not perceive any loss in the quality of service. A prototype implementation is under construction and the current version is available for download. Copyright

On the insufficiency of ontologies: problems in knowledge sharing and alternative solutions

One of the benefits of formally represented knowledge lies in its potential to be shared. Ontologies have been proposed as the ultimate solution to problems in knowledge sharing. However even when an agreed correspondence between ontologies is reached that is not the end of the problems in knowledge sharing. In this paper we explore a number of realistic knowledge-sharing situations and their related problems for which ontologies fall short in providing a solution. For each situation we propose and analyse alternative solutions.

Combining Temporal Logic Systems

This paper investigates modular combinations of temporal logic systems. Four combination methods are described and studied with respect to the transfer of logical properties from the component one-dimensional temporal logics to the resulting combined two-dimensional temporal logic. Three basic logical properties are analyzed, namely soundness, completeness, and decidability. Each combination method comprises three submethods that combine the languages, the inference systems, and the semantics of two onedimensional temporal logic systems, generating families of two-dimensional temporal languages with varying expressivity and varying degrees of transfer of logical properties. The temporalization method and the independent combination method are shown to transfer all three basic logical properties. The method of full join of logic systems generates a considerably more expressive language but fails to transfer completeness and decidability in several cases. So a weaker method of restricted join is proposed and shown to transfer all three basic logical properties.

Probabilistic satisfiability: logic-based algorithms and phase transition

In this paper, we study algorithms for probabilistic satisfiability (PSAT), an NP-complete problem, and their empiric complexity distribution. We define a PSAT normal form, based on which we propose two logic-based algorithms: a reduction of normal form PSAT instances to SAT, and a linearalgebraic algorithmwith a logic-based column generation strategy. We conclude that both algorithms present a phase transition behaviour and that the latter has a much better performance.

Handling database updates in two-dimensional temporal logic

This paper deals with the description of the evolution of the understanding of the history of a particular world. We have particular interest in describing certain problems that occur in database systems due to updates. For this purpose, we introduce a two-dimensional temporal logic as a formalism which enables the description of both the history and the evolution of the beliefs about the history. The historical dimension describes the history of the world according to a certain belief. The belief dimension describes the evolution of those beliefs. The historical dimension is then associated with an historical database, and transactions in the database are associated with changes in belief. Besides describing the history of the world, the database system can also execute temporal speciications in the form of temporal actions. The two-dimensional formalism is used to describe the eeects of updates in the execution of temporal actions. Those descriptions are then taken as speciications for a database system and their implementation is discussed.

Approximate and Limited Reasoning: Semantics, Proof Theory, Expressivity and Control

Real agents (natural or artificial) are limited in their reasoning capabilities. In this paper, we present a general framework for modelling limited reasoning based on approximate reasoning and discuss its properties. We start from Cadoli and Schaerfs approximate entailment. We first extend their system to deal with the full language of propositional logic. A tableau inference system is proposed for the extended system together with a subclassical semantics; it is shown that this new approximate reasoning system is sound and complete with respect to this semantics. We show how this system can be incrementally used to move from one approximation to the next until the reasoning limitation is reached. We also present a sound and complete axiomatization of the extended system. We note that although the extension is more expressive than the original system, it offers less control over the approximation process. We then propose a more general system and show that it keeps the increased expressivity and recovers the control. A sound and complete formulation for this new system is given and its expressivity and control advantages are formally proved.

The Unrestricted Combination of Temporal Logic Systems

This paper generalises and complements the work on combining temporal logics started by Finger and Gabbay [11, 10]. We present proofs of transference of soundness, completeness and decidability for the temporalisation of logics T(L) for any flow of time, eliminating the original restriction that required linear time for the transference of those properties through logic combination. We also generalise such results to the external application of a multi-modal system containing any number of connectives with arbitrary arity, that respect normality. This generalisation over generic flows of time propagates to other combinations of logics that can be interpreted in terms of temporalisations. In this way, the independent combination (also called fusion) of temporal logics is studied over generic flows of time. We show the transfer of soundness, completeness and decidability for independent combination of temporal logics. Finally, we also discuss the independent combination of any nite number of normal multi-modal logics.

Application execution management on the InteGrade opportunistic grid middleware

The InteGrade project is a multi-university effort to build a novel grid computing middleware based on the opportunistic use of resources belonging to user workstations. The InteGrade middleware currently enables the execution of sequential, bag-of-tasks, and parallel applications that follow the BSP or the MPI programming models. This article presents the lessons learned over the last five years of the InteGrade development and describes the solutions achieved concerning the support for robust application execution. The contributions cover the related fields of application scheduling, execution management, and fault tolerance. We present our solutions, describing their implementation principles and evaluation through the analysis of several experimental results.

Measuring inconsistency in probabilistic logic

Consistency, independence and continuity are incompatible postulates.Minimal inconsistent sets are not suitable to analyze probabilistic incon-sistencies.Independence can be weakened considering the underlying consolidation process.Inconsistency and incoherence measures based on distances and Dutch books coincide. Inconsistency measures have been proposed as a way to manage inconsistent knowledge bases in the AI community. To deal with inconsistencies in the context of conditional probabilistic logics, rationality postulates and computational efficiency have driven the formulation of inconsistency measures. Independently, investigations in formal epistemol-ogy have used the betting concept of Dutch book to measure an agents degree of incoherence. In this paper, we show the impossibility of joint satisfiability of the proposed postulates, proposing to replace them by more suitable ones. Thus we reconcile the rationality postulates for inconsistency measures in probabilistic bases and show that several inconsistency measures suggested in the literature and computable with linear programs satisfy the reconciled postulates. Additionally, we give an interpretation for these feasible measures based on the formal epistemology concept of Dutch book, bridging the views of two so far separate communities in AI and Philosophy. In particular, we show that incoherence degrees in formal epistemology may lead to novel approaches to inconsistency measures in the AI view.