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42
Parameter learning of logic programs for symbolicstatistical modeling
 Journal of Artificial Intelligence Research
, 2001
"... We propose a logical/mathematical framework for statistical parameter learning of parameterized logic programs, i.e. de nite clause programs containing probabilistic facts with a parameterized distribution. It extends the traditional least Herbrand model semantics in logic programming to distributio ..."
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Cited by 92 (19 self)
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We propose a logical/mathematical framework for statistical parameter learning of parameterized logic programs, i.e. de nite clause programs containing probabilistic facts with a parameterized distribution. It extends the traditional least Herbrand model semantics in logic programming to distribution semantics, possible world semantics with a probability distribution which is unconditionally applicable to arbitrary logic programs including ones for HMMs, PCFGs and Bayesian networks. We also propose a new EM algorithm, the graphical EM algorithm, thatrunsfora class of parameterized logic programs representing sequential decision processes where each decision is exclusive and independent. It runs on a new data structure called support graphs describing the logical relationship between observations and their explanations, and learns parameters by computing inside and outside probability generalized for logic programs. The complexity analysis shows that when combined with OLDT search for all explanations for observations, the graphical EM algorithm, despite its generality, has the same time complexity as existing EM algorithms, i.e. the BaumWelch algorithm for HMMs, the InsideOutside algorithm for PCFGs, and the one for singly connected Bayesian networks that have beendeveloped independently in each research eld. Learning experiments with PCFGs using two corpora of moderate size indicate that the graphical EM algorithm can signi cantly outperform the InsideOutside algorithm. 1.
An abstract machine for computing the wellfounded semantics
 Proceedings of the Joint International Conference and Symposium on Logic Programming
, 1996
"... The wellfounded semantics has gained wide acceptance partly because it is a skeptical semantics. That is, the wellfounded model posits as unknown atoms which are deemed true or false in other formalisms such as stable models. This skepticism makes the wellfounded model not only useful in itself, ..."
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Cited by 31 (17 self)
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The wellfounded semantics has gained wide acceptance partly because it is a skeptical semantics. That is, the wellfounded model posits as unknown atoms which are deemed true or false in other formalisms such as stable models. This skepticism makes the wellfounded model not only useful in itself, but also suitable as a basis for other forms of nonmonotonic reasoning. For instance, since algorithms to compute stable models are intractable, the atoms relevant tosuch algorithms can be limited to those unde ned in the wellfounded model. This paper presents an implementation ofthewellfounded semantics in the SLGWAM of XSB. To compute the wellfounded semantics, the SLGWAM adds three operations to its tabling engine  negative loop detection, delay and simplication  which serve to detect, to break and to resolve cycles through negation that may arise in evaluating normal programs. We describe fully the addition of these operations to our tabling engine, and demonstrate the e ciency of our implementation in two ways. First, we present a theorem that bounds the need for delay to those literals which are not dynamically strati ed for a xedorder computation. Secondly, we present performance results that indicate that the overhead of delay and simpli cation to Prolog  or tabled  evaluations is minimal. 1
Tabled HigherOrder Logic Programming
 In 20th International Conference on Automated Deduction
, 2003
"... Elf is a general metalanguage for the specification and implementation of logical systems in the style of the logical framework LF. Based on a logic programming interpretation, it supports executing logical systems and reasoning with and about them, thereby reducing the effort required for each ..."
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Cited by 26 (11 self)
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Elf is a general metalanguage for the specification and implementation of logical systems in the style of the logical framework LF. Based on a logic programming interpretation, it supports executing logical systems and reasoning with and about them, thereby reducing the effort required for each particular logical system. The traditional logic programming paradigm is extended by replacing firstorder terms with dependently typed terms and allowing implication and universal quantification in the bodies of clauses. These higherorder features allow us to model concisely and elegantly conditions on variables and the discharge of assumptions which are prevalent in many logical systems. However, many specifications are not executable under the traditional logic programming semantics and performance may be hampered by redundant computation. To address these problems, I propose a tabled higherorder logic programming interpretation for Elf. Some redundant computation is eliminated by memoizing subcomputation and reusing its result later. If we do not distinguish different proofs for a property, then search based on tabled logic programming is complete and terminates for programs with bounded recursion. In this proposal, I present a prooftheoretical characterization for tabled higherorder logic programming. It is the basis of the implemented prototype for tabled logic programming interpreter for Elf. Preliminary experiments indicate that many more logical specifications are executable under the tabled semantics. In addition, tabled computation leads to more efficient execution of programs. The goal of the thesis is to demonstrate that tabled logic programming allows us to efficiently automate reasoning with and about logical systems in the logical f...
Prologbased Infrastructure for RDF: Scalability and Performance
 In: The SemanticWeb  ISWC 2003
, 2003
"... The semantic web is a promising applicationarea for the Prolog programming language for its nondeterminism and patternmatching. In this paper we outline an infrastructure for loading and saving RDF/XML, storing triples, elementary reasoning with triples and visualization. A predecessor of the inf ..."
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Cited by 15 (3 self)
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The semantic web is a promising applicationarea for the Prolog programming language for its nondeterminism and patternmatching. In this paper we outline an infrastructure for loading and saving RDF/XML, storing triples, elementary reasoning with triples and visualization. A predecessor of the infrastructure described here has been used in various applications for ontologybased annotation of multimedia objects using semantic web languages. Our library aims at fast parsing, fast access and scalability for fairly large but not unbounded applications upto 40 million triples.
Preserving Termination of Tabled Logic Programs While Unfolding
 In Proc. of the 7th Int’l Workshop on Logic Programming Synthesis and Transformation (LOPSTR’97
, 1997
"... We provide a first investigation of the specialisation and transformation of tabled logic programs through unfolding. We show that  surprisingly  unfolding, even determinate, can worsen the termination behaviour in the context of tabling. We therefore establish two criteria which ensure that s ..."
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Cited by 15 (9 self)
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We provide a first investigation of the specialisation and transformation of tabled logic programs through unfolding. We show that  surprisingly  unfolding, even determinate, can worsen the termination behaviour in the context of tabling. We therefore establish two criteria which ensure that such mishaps are avoided. We also briefly discuss the influence of some other transformation techniques on the termination and efficiency of tabled logic programs.
Understanding Memory Management in Prolog Systems
 In International Conference on Logic Programming, number 2237 in LNCS
, 2001
"... Actual performance of Prolog based applications largely depends on how the underlying system implements memory management. ..."
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Cited by 13 (5 self)
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Actual performance of Prolog based applications largely depends on how the underlying system implements memory management.
Universal regular path queries
 HigherOrder and Symbolic Computation
, 2003
"... Given are a directed edgelabelled graph G with a distinguished node n0, and a regular expression P which may contain variables. We wish to compute all substitutions φ (of symbols for variables), together with all nodes n such that all paths n0 → n are in φ(P). We derive an algorithm for this proble ..."
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Cited by 13 (1 self)
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Given are a directed edgelabelled graph G with a distinguished node n0, and a regular expression P which may contain variables. We wish to compute all substitutions φ (of symbols for variables), together with all nodes n such that all paths n0 → n are in φ(P). We derive an algorithm for this problem using relational algebra, and show how it may be implemented in Prolog. The motivation for the problem derives from a declarative framework for specifying compiler optimisations. 1 Bob Paige and IFIP WG 2.1 Bob Paige was a longstanding member of IFIP Working Group 2.1 on Algorithmic Languages and Calculi. In recent years, the main aim of this group has been to investigate the derivation of algorithms from specifications by program transformation. Already in the mideighties, Bob was way ahead of the pack: instead of applying transformational techniques to wellworn examples, he was applying his theories of program transformation to new problems, and discovering new algorithms [16, 48, 52]. The secret of his success lay partly in his insistence on the study of general algorithm design strategies (in particular
SemanticsBased Program Analysis for LogicBased Languages Using XSB
, 1998
"... This article describes a simple and ecient way of using a logic programming language with builtin tabulation for general purpose semanticsbased program analysis. The simplicity of the method is based on a clear separation of abstraction and control: conceptually, a concrete program is executed ove ..."
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Cited by 12 (7 self)
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This article describes a simple and ecient way of using a logic programming language with builtin tabulation for general purpose semanticsbased program analysis. The simplicity of the method is based on a clear separation of abstraction and control: conceptually, a concrete program is executed over an abstract domain and the tabulation mechanism avoids recomputation, ensures termination and collects the results of the analysis. The efficiency derives from the fact that an abstract interpreter induces an abstract compiler which maps input programs to corresponding abstract programs which are (compiled and) run in XSB [43]. The design of new analyses is an easy and fast process, because XSB is a general purpose logic programming system which supports efficient fixpoint computations through tabling implemented at the abstract machine level and comes off the shelf: in fact, due to its optimized control and superior tabling performance, our approach using XSB competitively compares with most of the existing special purpose abstract interpretation tools for logic programs. We demonstrate that our approach to using XSB for abstract interpretation supports the usual techniques and optimizations of other frameworks in a straightforward and flexible way.
A Thread in Time Saves Tabling Time
 In Joint International Conference/Symposium on Logic Programming
, 1996
"... The use of tabling in logic programming has been recognized as a powerful evaluation technique. Currently available tabling systems are mostly based on variant checks and hence are limited in their ability to recognize reusable subcomputations. Tabling systems based on call subsumption can yield sup ..."
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Cited by 11 (4 self)
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The use of tabling in logic programming has been recognized as a powerful evaluation technique. Currently available tabling systems are mostly based on variant checks and hence are limited in their ability to recognize reusable subcomputations. Tabling systems based on call subsumption can yield superior performance by recognizing a larger set of reusable computations. However, a straightforward adaptation of the mechanisms used in variantbased systems to reuse these computations can in fact result in considerable performance degradation. In this paper we propose a novel organization of tables using Dynamic Threaded Sequential Automata (DTSA) which permits efficient reuse of previously computed results in a subsumptive system. We describe an implementation of the tables using DTSA and the associated access mechanisms. We also report experimental results which show that a subsumptive tabling system implemented by extending the XSB logic programmingsystem with our table access techniqu...