Results 1  10
of
13
Improvements To Propositional Satisfiability Search Algorithms
, 1995
"... ... quickly across a wide range of hard SAT problems than any other SAT tester in the literature on comparable platforms. On a Sun SPARCStation 10 running SunOS 4.1.3 U1, POSIT can solve hard random 400variable 3SAT problems in about 2 hours on the average. In general, it can solve hard nvariable ..."
Abstract

Cited by 161 (0 self)
 Add to MetaCart
... quickly across a wide range of hard SAT problems than any other SAT tester in the literature on comparable platforms. On a Sun SPARCStation 10 running SunOS 4.1.3 U1, POSIT can solve hard random 400variable 3SAT problems in about 2 hours on the average. In general, it can solve hard nvariable random 3SAT problems with search trees of size O(2 n=18:7 ). In addition to justifying these claims, this dissertation describes the most significant achievements of other researchers in this area, and discusses all of the widely known general techniques for speeding up SAT search algorithms. It should be useful to anyone interested in NPcomplete problems or combinatorial optimization in general, and it should be particularly useful to researchers in either Artificial Intelligence or Operations Research.
Directed Hypergraphs And Applications
, 1992
"... We deal with directed hypergraphs as a tool to model and solve some classes of problems arising in Operations Research and in Computer Science. Concepts such as connectivity, paths and cuts are defined. An extension of the main duality results to a special class of hypergraphs is presented. Algorith ..."
Abstract

Cited by 100 (5 self)
 Add to MetaCart
We deal with directed hypergraphs as a tool to model and solve some classes of problems arising in Operations Research and in Computer Science. Concepts such as connectivity, paths and cuts are defined. An extension of the main duality results to a special class of hypergraphs is presented. Algorithms to perform visits of hypergraphs and to find optimal paths are studied in detail. Some applications arising in propositional logic, AndOr graphs, relational data bases and transportation analysis are presented. January 1990 Revised, October 1992 ( * ) This research has been supported in part by the "Comitato Nazionale Scienza e Tecnologia dell'Informazione", National Research Council of Italy, under Grant n.89.00208.12, and in part by research grants from the National Research Council of Canada. 1 Dipartimento di Informatica, Università di Pisa, Italy 2 Département d'Informatique et de Recherche Opérationnelle, Université de Montréal, Canada 2 INTRODUCTION Hypergraphs, a generaliz...
Logic and Databases: a 20 Year Retrospective
, 1996
"... . At a workshop held in Toulouse, France in 1977, Gallaire, Minker and Nicolas stated that logic and databases was a field in its own right (see [131]). This was the first time that this designation was made. The impetus for this started approximately twenty years ago in 1976 when I visited Gallaire ..."
Abstract

Cited by 55 (1 self)
 Add to MetaCart
. At a workshop held in Toulouse, France in 1977, Gallaire, Minker and Nicolas stated that logic and databases was a field in its own right (see [131]). This was the first time that this designation was made. The impetus for this started approximately twenty years ago in 1976 when I visited Gallaire and Nicolas in Toulouse, France, which culminated in a workshop held in Toulouse, France in 1977. It is appropriate, then to provide an assessment as to what has been achieved in the twenty years since the field started as a distinct discipline. In this retrospective I shall review developments that have taken place in the field, assess the contributions that have been made, consider the status of implementations of deductive databases and discuss the future of work in this area. 1 Introduction As described in [234], the use of logic and deduction in databases started in the late 1960s. Prominent among the developments was the work by Levien and Maron [202, 203, 199, 200, 201] and Kuhns [1...
Computing the WellFounded Semantics Faster
, 1995
"... . We address methods of speeding up the calculation of the wellfounded semantics for normal propositional logic programs. We first consider two algorithms already reported in the literature and show that these, plus a variation upon them, have much improved worstcase behavior for special cases ..."
Abstract

Cited by 23 (0 self)
 Add to MetaCart
. We address methods of speeding up the calculation of the wellfounded semantics for normal propositional logic programs. We first consider two algorithms already reported in the literature and show that these, plus a variation upon them, have much improved worstcase behavior for special cases of input. Then we propose a general algorithm to speed up the calculation for logic programs with at most two positive subgoals per clause, intended to improve the worst case performance of the computation. For a logic program P in atoms A, the speed up over the straight Van Gelder alternating fixed point algorithm (assuming worstcase behavior for both algorithms) is approximately (jPj=jAj) (1=3) . For jPj jAj 4 , the algorithm runs in time linear in jPj. 1 Introduction Logic programming researchers have, over the last several years, proposed many logicbased declarative semantics for various sorts of logic programming. The hope is that, if they can be efficiently implemented, t...
Disjunctive Logic Programming: A Survey And Assessment
, 2002
"... We describe the elds of disjunctive logic programming and disjunctive deductive databases from the time of their inception to the current time. Contributions with respect to semantics, implementations and applications are surveyed. ..."
Abstract

Cited by 16 (0 self)
 Add to MetaCart
We describe the elds of disjunctive logic programming and disjunctive deductive databases from the time of their inception to the current time. Contributions with respect to semantics, implementations and applications are surveyed.
Directed Hypergraphs as a Modelling Paradigm
 RIVISTA AMASES
, 1999
"... We address a generalization of graphs, the directed hypergraphs, and show that they are a powerful tool in modelling and solving several relevant problems in many application areas. Such application areas include Linear Production Problems, Flexible Manufacturing Systems, Propositional Logic, Relat ..."
Abstract

Cited by 12 (1 self)
 Add to MetaCart
We address a generalization of graphs, the directed hypergraphs, and show that they are a powerful tool in modelling and solving several relevant problems in many application areas. Such application areas include Linear Production Problems, Flexible Manufacturing Systems, Propositional Logic, Relational Databases, and Public Transportation Systems.
Some Remarks on Computability and Open Domain Semantics
 In Proc. of the Worksh. on Struct. Complexity and RecursionTheoretic Methods in Log. Prog
, 1993
"... this paper is in questions of decidability and tractability for open domain specifications  open domain specifications using the finite open domain and arbitrarily large open domain hypotheses. For some corresponding results for the infinite open domain assumption we refer the reader to our paper ..."
Abstract

Cited by 10 (0 self)
 Add to MetaCart
this paper is in questions of decidability and tractability for open domain specifications  open domain specifications using the finite open domain and arbitrarily large open domain hypotheses. For some corresponding results for the infinite open domain assumption we refer the reader to our paper [19]
Average Case Results for Satisfiability Algorithms Under the Random Clause Width Model
 Annals of Mathematics and Artificial Intelligence
, 1995
"... In the probabilistic analysis of algorithms for the Satisfiability problem, the randomclausewidth model is one of the most popular for generating random instances. This model is parameterized and it is not difficult to show that virtually the entire parameter space is covered by a collection of ..."
Abstract

Cited by 9 (1 self)
 Add to MetaCart
In the probabilistic analysis of algorithms for the Satisfiability problem, the randomclausewidth model is one of the most popular for generating random instances. This model is parameterized and it is not difficult to show that virtually the entire parameter space is covered by a collection of polynomial time algorithms that find solutions to random instances with probability tending to 1 as instance size increases. But finding a collection of polynomial average time algorithms that cover the parameter space has proved much harder and such results have spanned approximately ten years. However, it can now be said that virtually the entire parameter space is covered by polynomial average time algorithms. This paper relates dominant, exploitable properties of random formulas over the parameter space to mechanisms of polynomial average time algorithms. The probabilistic discussion of such properties is new; main averagecase results over the last ten years are reviewed. 1 Intr...
Unique Satisfiability of Horn Sets Can Be Solved in Nearly Linear Time
 In Discrete Applied Mathematics
, 1995
"... If a Horn set I has a single satisfying truth assignment or model then that model is said to be unique for I. The question of determining whether a unique model exists for a given Horn set I is shown to be solved in O(ff(L) L) time, where L is the sum of the lengths of the clauses in I and ff is ..."
Abstract

Cited by 3 (1 self)
 Add to MetaCart
If a Horn set I has a single satisfying truth assignment or model then that model is said to be unique for I. The question of determining whether a unique model exists for a given Horn set I is shown to be solved in O(ff(L) L) time, where L is the sum of the lengths of the clauses in I and ff is the inverse Ackermann function. It is also shown that if L A log(A) where A is the number of distinct proposition letters then unique satisfiability can be determined in O(L) time. 1 Introduction Sets of Horn clauses are wellknown to be computationally much more tractable than sets of arbitrary clauses. For example, satisfiability for sets of Horn clauses of propositional logic can be determined in linear time, whereas satisfiability for sets of arbitrary clauses of propositional logic is NPhard. Unique satisfiability on Horn sets is one problem that can be solved in quadratic time [7] even though the general problem is coNP hard [5]. Using ideas based on those of [7], we can improv...
Y.: Hilbertian deductive systems, infon logic, and Datalog
 Bull. of Euro. Assoc. for Theor. Computer Sci
, 2010
"... In the first part of the paper, we develop a general method for converting derivability problems, from a broad range of deductive systems, into derivability problems in a quite specific system, namely the Datalog fragment of universal Horn logic. In this generality, the derivability problems may not ..."
Abstract

Cited by 2 (1 self)
 Add to MetaCart
In the first part of the paper, we develop a general method for converting derivability problems, from a broad range of deductive systems, into derivability problems in a quite specific system, namely the Datalog fragment of universal Horn logic. In this generality, the derivability problems may not be recursively solvable, let alone feasible; in particular, we may get Datalog “programs ” with infinitely many rules. We then discuss what would be needed to obtain computationally useful results from this method. In the second part of the paper, we analyze a particular deductive system, primal infon logic with variables, which arose in the development of the authorization language DKAL. A consequence of our analysis of primal infon logic with variables is that its derivability problems can be translated into Datalog with only a linear increase of size.