Abstract
Inference in many probabilistic logic systems is based on representing the proofs of a query as a DNF Boolean formula. Assessing the probability of such a formula is known as a #P-hard task. In practice, a large DNF is given to a BDD software package to construct the corresponding BDD. The DNF has to be transformed into the input format of the package. This is the preprocessing step. In this paper we investigate and compare different preprocessing methods, including our new trie based approach. Our experiments within the ProbLog system show that the behaviour of the methods changes according to the amount of sharing in the original DNF. The decomposition method is preferred when there is not much sharing in the DNF, whereas DNFs with sharing benefit from our trie based method. While our methods are motivated and applied in the ProbLog context, our results are interesting for other applications that manipulate DNF Boolean formulae.

Abstract
Tabled evaluation is a recognized and powerful implementation technique that overcomes some limitations of traditional Prolog systems in dealing with recursion and redundant sub-computations. Tabling based systems use call similarity to determine if a tabled subgoal will produce their own answers or if it will consume from another subgoal. While call variance has been a very popular approach, call subsumption can yield superior time performance and space improvements as it allows greater reuse of answers. However, the call order of the subgoals can greatly affect the success and applicability of the call subsumption technique. In this work, we present an extension, named Retroactive Call Subsumption, that supports call subsumption by allowing full sharing of answers between subsumed/subsuming subgoals, independently on the order in which they are called. Our experiments using the YapTab tabling engine show considerable gains in evaluation time for some applications, at the expense of a very small overhead for the programs that cannot benefit from it.

Abstract
Tabling is a technique of resolution that overcomes some limitations of traditional Prolog systems in dealing with recursion and redundant sub-computations. We can distinguish two main categories of tabling mechanisms: suspension-based tabling and linear tabling. In suspension-based tabling, a tabled evaluation can be seen as a sequence of sub-computations that suspend and later resume. Linear tabling mechanisms maintain a single execution tree where tabled subgoals always extend the current computation without requiring suspension and resumption of sub-computations. In this work, we present a new and efficient implementation of linear tabling, but for that we have extended an already existent suspension-based implementation, the YapTab engine. Our design is based on dynamic reordering of alternatives but it innovates by considering a strategy that schedules the re-evaluation of tabled calls in a similar manner to the suspension-based strategies of YapTab. Our implementation also shares the underlying execution environment and most of the data structures used to implement tabling in YapTab. We thus argue that all these common features allows us to make a first and fair comparison between suspension-based and linear tabling and, therefore, better understand the advantages and weaknesses of each.

Abstract
A critical component in the implementation of an efficient tabling system is the design of the data structures and algorithms to access and manipulate tabled data. Arguably, the most successful data structure for tabling is tries, which is regarded as a very compact and efficient; data structure for term representation. Despite these good properties, we found that, for list terms, we can design even more compact and efficient representations. We thus propose a, new representation of list terms for tries that avoids the recursive nature of the WAM representation of list terms in which tries are based. Our experimental results using the YapTab tabling system show a significant reduction in the memory usage for the trie data structures and considerable gains in the running time for storing and loading list terms.

Abstract
(Non-)portability of Prolog programs is widely considered as an important factor in the lack of acceptance of the language. Since 1995, the core of the language is covered by the ISO standard 13211-1. Since 2007, YAP and SWI-Prolog have established a basic compatibility framework. This article describes and evaluates this framework. The aim of the framework is running the same code on both systems rather than migrating an application. We show that today, the portability within the family of Edinburgh/Quintus derived Prolog implementations is good enough to allow for maintaining portable real-world applications.

Abstract
We study how probabilistic reasoning and inductive querying can be combined within ProbLog, a recent probabilistic extension of Prolog. ProbLog can be regarded as a database system that supports both probabilistic and inductive reasoning through a variety of querying mechanisms. After a short introduction to ProbLog, we provide a survey of the different types of inductive queries that ProbLog supports, and show how it can be applied to the mining of large biological networks. © 2010 Springer Science+Business Media, LLC.