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31
Unfold/fold transformations of CCP programs
 ACM Transactions on Programming Languages and Systems
, 1998
"... We introduce a transformation system for concurrent constraint programming (CCP). We define suitable applicability conditions for the transformations which guarantee that the input/output CCP semantics is preserved also when distinguishing deadlocked computations from successful ones and when consid ..."
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Cited by 19 (5 self)
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We introduce a transformation system for concurrent constraint programming (CCP). We define suitable applicability conditions for the transformations which guarantee that the input/output CCP semantics is preserved also when distinguishing deadlocked computations from successful ones and when considering intermediate results of (possibly) nonterminating computations. The system allows us to optimize CCP programs while preserving their intended meaning: In addition to the usual benefits that one has for sequential declarative languages, the transformation of concurrent programs can also lead to the elimination of communication channels and of synchronization points, to the transformation of nondeterministic computations into deterministic ones, and to the crucial saving of computational space. Furthermore, since the transformation system preserves the deadlock behavior of programs, it can be used for proving deadlock freeness of a given program with respect to a class of queries. To this aim it is sometimes sufficient to apply our transformations and to specialize the resulting program with respect to the given queries in such a way that the obtained program is trivially deadlock free.
Some (in)translatability results for normal logic programs and propositional theories
 Journal of Applied NonClassical Logics
, 2006
"... ABSTRACT. In this article, we compare the expressive powers of classes of normal logic programs that are obtained by constraining the number of positive subgoals (n) in the bodies of rules. The comparison is based on the existence/nonexistence of polynomial, faithful, and modular (PFM) translation f ..."
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Cited by 16 (6 self)
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ABSTRACT. In this article, we compare the expressive powers of classes of normal logic programs that are obtained by constraining the number of positive subgoals (n) in the bodies of rules. The comparison is based on the existence/nonexistence of polynomial, faithful, and modular (PFM) translation functions between the classes. As a result, we obtain a strict ordering among the classes under consideration. Binary programs (n ≤ 2) are shown to be as expressive as unconstrained programs but strictly more expressive than unary programs (n ≤ 1) which, in turn, are strictly more expressive than atomic programs (n = 0). We also take propositional theories into consideration and prove them to be strictly less expressive than atomic programs. In spite of the gap in expressiveness, we develop a faithful but nonmodular translation function from normal programs to propositional theories. We consider this as a breakthrough due to subquadratic time complexity (of the order of P   × log 2 Hb(P)). Furthermore, we present a prototype implementation of the translation function and demonstrate its promising performance with SAT solvers using three benchmark problems.
Transformation of Left Terminating Programs: The Reordering Problem
 PROCEEDINGS LOPSTR'95, VOLUME 1048 OF LECTURE NOTES IN COMPUTER SCIENCE
, 1995
"... An Unfold/Fold transformation system is a sourcetosource rewriting methodology devised to improve the efficiency of a program. Any such transformation should preserve the main properties of the initial program: among them, termination. When dealing with logic programs such as PROLOG programs, on ..."
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Cited by 15 (3 self)
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An Unfold/Fold transformation system is a sourcetosource rewriting methodology devised to improve the efficiency of a program. Any such transformation should preserve the main properties of the initial program: among them, termination. When dealing with logic programs such as PROLOG programs, one is particularly interested in preserving left termination i.e. termination wrt the leftmost selection rule, which is by far the most widely employed of the search rules. Unfortunately, the most popular Unfold/Fold transformation systems ([TS84, Sek91]) do not preserve the above termination property. In this paper we study the reasons why left termination may be spoiled by the application of a transformation operation and we present a transformation system based on the operations of Unfold, Fold and Switch which if applied to a left terminating programs yields a program which is left terminating as well.
Transformation Rules for Locally Stratified Constraint Logic Programs
, 2004
"... We propose a set of transformation rules for constraint logic programs with negation. We assume that every program is locally strati ed and, thus, it has a unique perfect model. We give sucient conditions which ensure that the proposed set of transformation rules preserves the perfect model of ..."
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Cited by 14 (13 self)
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We propose a set of transformation rules for constraint logic programs with negation. We assume that every program is locally strati ed and, thus, it has a unique perfect model. We give sucient conditions which ensure that the proposed set of transformation rules preserves the perfect model of the programs. Our rules extend in some respects the rules for logic programs and constraint logic programs already considered in the literature and, in particular, they include a rule for unfolding a clause with respect to a negative literal.
A Transformation System for CLP with Dynamic Scheduling and ccp
 In Proc. of the ACM Sigplan PEPM’97
, 1997
"... In this paper we study unfold/fold transformations for constraint logic programs (CLP) with dynamic scheduling and for concurrent constraint programming (ccp). We define suitable applicability conditions for this transformations which ensure us that the original and the transformed program have the ..."
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Cited by 11 (2 self)
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In this paper we study unfold/fold transformations for constraint logic programs (CLP) with dynamic scheduling and for concurrent constraint programming (ccp). We define suitable applicability conditions for this transformations which ensure us that the original and the transformed program have the same results of successful computations and have the same deadlocked derivations. The possible applications of these results are twofold. On one hand we can use the unfold/fold system to optimize CLP and ccp programs while preserving their intended meaning and in particular without the risk of introducing deadlocks. On the other hand, unfold/fold transformations can be used for proving deadlock freedom for a class of queries in a given program: to this aim it is sufficient to specialize the program with respect to the given queries in such a way that the resulting program is trivially deadlock free. As shown by several interesting examples, this yields a methodology for proving deadlock free...
Automated Strategies for Specializing Constraint Logic Programs
 LOPSTR 2000, LNCS 2042
"... We consider the problem of specializing constraint logic programs w.r.t. constrained queries. We follow a transformational approach based on rules and strategies. The use of the rules ensures that the specialized program is equivalent to the initial program w.r.t. a given constrained query. The stra ..."
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Cited by 10 (8 self)
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We consider the problem of specializing constraint logic programs w.r.t. constrained queries. We follow a transformational approach based on rules and strategies. The use of the rules ensures that the specialized program is equivalent to the initial program w.r.t. a given constrained query. The strategies guide the application of the rules so to derive an efficient specialized program. In this paper we address various issues concerning the development of an automated transformation strategy. In particular, we consider the problems of when and how we should unfold, replace constraints, introduce generalized clauses, and apply the contextual constraint replacement rule. We propose a solution to these problems by adapting to our framework various techniques developed in the field of constraint programming, partial evaluation, and abstract interpretation. In particular, we use: (i) suitable solvers for simplifying constraints, (ii) wellquasiorders for ensuring the termination...
Specialization with Clause Splitting for Deriving Deterministic Constraint Logic Programs
 In Proc. IEEE Conference on Systems, Man and Cybernetics, Hammamet
, 2002
"... The reduction of nondeterminism can increase efficiency when specializing programs. We consider constraint logic programs and we propose a technique which by making use of a new transformation rule, called clause splitting, allows us to generate efficient, specialized programs which are deterministi ..."
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Cited by 5 (5 self)
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The reduction of nondeterminism can increase efficiency when specializing programs. We consider constraint logic programs and we propose a technique which by making use of a new transformation rule, called clause splitting, allows us to generate efficient, specialized programs which are deterministic. We have applied our technique to the specialization of pattern matching programs.
Proving properties of constraint logic programs by eliminating existential variables
 In Proc. ICLP ’06, LNCS 4079
, 2006
"... Abstract. We propose a method for proving rst order properties of constraint logic programs which manipulate nite lists of real numbers. Constraints are linear equations and inequations over reals. Our method consists in converting any given rst order formula into a strati ed constraint logic progra ..."
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Cited by 5 (5 self)
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Abstract. We propose a method for proving rst order properties of constraint logic programs which manipulate nite lists of real numbers. Constraints are linear equations and inequations over reals. Our method consists in converting any given rst order formula into a strati ed constraint logic program and then applying a suitable unfold/fold transformation strategy that preserves the perfect model. Our strategy is based on the elimination of existential variables, that is, variables which occur in the body of a clause and not in its head. Since, in general, the rst order properties of the class of programs we consider are undecidable, our strategy is necessarily incomplete. However, experiments show that it is powerful enough to prove several nontrivial program properties. 1
Program Derivation = Rules + Strategies
 Computational Logic: Logic Programming and Beyond (Essays in honour of Bob Kowalski, Part I), Lecture Notes in Computer Science 2407
, 2001
"... In a seminal paper [38] Prof. Robert Kowalski advocated the paradigm Algorithm = Logic + Control which was intended to characterize program executions. Here we want to illustrate the corresponding paradigm Program Derivation = Rules + Strategies which is intended to characterize program derivations, ..."
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Cited by 4 (2 self)
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In a seminal paper [38] Prof. Robert Kowalski advocated the paradigm Algorithm = Logic + Control which was intended to characterize program executions. Here we want to illustrate the corresponding paradigm Program Derivation = Rules + Strategies which is intended to characterize program derivations, rather than executions. During program execution, the Logic component guarantees that the computed results are correct, that is, they are true facts in the intended model of the given program, while the Control component ensures that those facts are derived in an efficient way. Likewise, during program derivation, the Rules component guarantees that the derived programs are correct and the Strategies component ensures that the derived programs are efficient.