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13
Satbased answer set programming
 In Proc. AAAI04
, 2004
"... The relation between answer set programming (ASP) and propositional satisfiability (SAT) is at the center of many research papers, partly because of the tremendous performance boost of SAT solvers during last years. Various translations from ASP to SAT are known but the resulting SAT formula either ..."
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Cited by 32 (8 self)
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The relation between answer set programming (ASP) and propositional satisfiability (SAT) is at the center of many research papers, partly because of the tremendous performance boost of SAT solvers during last years. Various translations from ASP to SAT are known but the resulting SAT formula either includes many new variables or may have an unpractical size. There are also well known results showing a onetoone correspondence between the answer sets of a logic program and the models of its completion. Unfortunately, these results only work for specific classes of problems. In this paper we present a SATbased decision procedure for answer set programming that (i) deals with any (non disjunctive) logic program, (ii) works on a SAT formula without additional variables, and (iii) is guaranteed to work in polynomial space. Further, our procedure can be extended to compute all the answer sets still working in polynomial space. The experimental results of a prototypical implementation show that the approach can pay off sometimes by orders of magnitude.
Distributed synthesis for wellconnected architectures
 FORM. METHODS SYST. DES
"... We study the synthesis problem for external linear or branching specifications and distributed, synchronous architectures with arbitrary delays on processes. External means that the specification only relates input and output variables. We introduce the subclass of uniformly wellconnected (UWC) ar ..."
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Cited by 9 (2 self)
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We study the synthesis problem for external linear or branching specifications and distributed, synchronous architectures with arbitrary delays on processes. External means that the specification only relates input and output variables. We introduce the subclass of uniformly wellconnected (UWC) architectures for which there exists a routing allowing each output process to get the values of all inputs it is connected to, as soon as possible. We prove that the distributed synthesis problem is decidable on UWC architectures if and only if the output variables are totally ordered by their knowledge of input variables. We also show that if we extend this class by letting the routing depend on the output process, then the previous decidability result fails. Finally, we provide a natural restriction on specifications under which the whole class of UWC architectures is decidable.
Safe Implementability of Regular Message Sequence Charts Specifications
 PROC. OF THE ACIS 4TH INT. CONF. SNDP
, 2003
"... Message Sequence Charts (MSCs) are drawn by software designers in order to model the typical behaviors of some communication protocol at an early stage of its design. The important question of whether some given set of scenarios is realizable by some message passing system has already been investiga ..."
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Cited by 8 (2 self)
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Message Sequence Charts (MSCs) are drawn by software designers in order to model the typical behaviors of some communication protocol at an early stage of its design. The important question of whether some given set of scenarios is realizable by some message passing system has already been investigated in different ways. We consider here deadlockfree implementations up to additional message contents. We present an algorithm to check safe implementability of MSC specifications in the framework of nonFIFO channels. Our criterion turns out to have the same complexity bounds as the restrictive approach of Alur et al. [1] where no additional message content is allowed.
The MSO Theory of Connectedly Communicating Processes
"... Abstract. We identify a network of sequential processes that communicate by synchronizing frequently on common actions. More precisely, we demand that there is a bound k such that if the process p executes k steps without hearing from process q—directly or indirectly—then it will neverhearfromq agai ..."
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Cited by 6 (0 self)
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Abstract. We identify a network of sequential processes that communicate by synchronizing frequently on common actions. More precisely, we demand that there is a bound k such that if the process p executes k steps without hearing from process q—directly or indirectly—then it will neverhearfromq again. The noninterleaved branching time behavior of a system of connectedly communicating processes (CCP) is given by its event structure unfolding. We show that the monadic second order (MSO) theory of the event structure unfolding of every CCP is decidable. Using this result, we also show that an associated distributed controller synthesis problem is decidable for linear time specifications that do not discriminate between two different linearizations of the same partially ordered execution.
Fast SATbased answer set solver
 In Proceedings of the Twentyfirst National Conference on Artificial Intelligence (AAAI’06
"... Recent research shows that SAT (propositional satisfiability) techniques can be employed to build efficient systems to compute answer sets for logic programs. ASSAT and CMODELS are two wellknown such systems. They find an answer set from the full models for the completion of the input program, whic ..."
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Cited by 5 (0 self)
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Recent research shows that SAT (propositional satisfiability) techniques can be employed to build efficient systems to compute answer sets for logic programs. ASSAT and CMODELS are two wellknown such systems. They find an answer set from the full models for the completion of the input program, which is (iteratively) augmented with loop formulas. Making use of the fact that, for nontight programs, during the model generation, a partial assignment may be extensible to a full model but may not grow into any answer set, we propose to add answer set extensibility checking on partial assignments. Furthermore, given a partial assignment, we identify a class of loop formulas that are “active ” on the assignment. These “active ” formulas can be used to prune the search space. We also provide an efficient method to generate these formulas. These ideas can be implemented with a moderate modification on SAT solvers. We have developed a new answer set solver SAG on top of the SAT solver MCHAFF. Empirical studies on wellknown benchmarks show that in most cases it is faster than the stateoftheart answer set solvers, often by an order of magnitude. In the few cases when it is not the winner, it is close to the top performer, which shows its robustness.
Twophase distributed observation problems
 in 5th Intl. Conf. on Application of Concurrency to System Design (ACSD’05). IEEE
, 2005
"... We introduce and study problems of distributed observation with bounded or unbounded memory. We are given a system modeled as a finiteword language L over some finite alphabet Σ and subalphabets Σ1,..., Σn of Σ modeling n distinct observation points. We want to build (when there exist) n observers ..."
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Cited by 4 (0 self)
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We introduce and study problems of distributed observation with bounded or unbounded memory. We are given a system modeled as a finiteword language L over some finite alphabet Σ and subalphabets Σ1,..., Σn of Σ modeling n distinct observation points. We want to build (when there exist) n observers which collect projections of a behavior in L onto Σ1,..., Σn, then send them to a central decision point. The latter must determine whether the original behavior was in a given K ⊆ L. In the unboundedmemory case, observers record the entire sequence they observe. In the boundedmemory case, they are required to be finitestate automata. We show that, when L is traceclosed with respect to the usual dependence relation induced by Σ1,..., Σn, unboundedmemory observability is equivalent to K being centrally observable and traceclosed, thus decidable. When L is not traceclosed, the problem is undecidable, even if K and L are regular. We also show that boundedmemory observability is equivalent to unboundedmemory observability (thus decidable) when L is traceclosed and Σi are pairwise disjoint. Otherwise, the problem remains open. In the decidable cases, observers and decision function can be automatically synthesized. 1
Constructing Exponentialsize Deterministic Zielonka Automata
 IN "ICALP", VOL. LNCS 4052
, 2006
"... The wellknown algorithm of Zielonka describes how to transform automatically a sequential automaton into a deterministic asynchronous trace automaton. In this paper, we improve the construction of deterministic asynchronous automata from finite state automaton. Our construction improves the wellk ..."
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Cited by 4 (1 self)
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The wellknown algorithm of Zielonka describes how to transform automatically a sequential automaton into a deterministic asynchronous trace automaton. In this paper, we improve the construction of deterministic asynchronous automata from finite state automaton. Our construction improves the wellknown construction in that the size of the asynchronous automaton is simply exponential in both the size of the sequential automaton and the number of processes. In contrast, Zielonka’s algorithm gives an asynchronous automaton that is doubly exponential in the number of processes (and simply exponential in the size of the automaton).
A SATbased polynomial space algorithm for answer set programming
 PROCEEDINGS OF THE TENTH INTERNATIONAL WORKSHOP ON NONMONOTONIC REASONING. (2004) 189–196
"... The relation between answer set programming (ASP) and propositional satisfiability (SAT) is at the center of many research papers, partly because of the tremendous performance boost of SAT solvers during last years. Various translations from ASP to SAT are known but the resulting SAT formula either ..."
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Cited by 3 (0 self)
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The relation between answer set programming (ASP) and propositional satisfiability (SAT) is at the center of many research papers, partly because of the tremendous performance boost of SAT solvers during last years. Various translations from ASP to SAT are known but the resulting SAT formula either includes many new variables or may have an unpractical size. There are also well known results showing a onetoone correspondence between the answer sets of a logic program and the models of its completion. Unfortunately, these results only work for specific classes of problems. In this paper we present a SATBased decision procedure for answer set programming that (i) deals with any (non disjunctive) logic program, (ii) works on a SAT formula without additional variables, and (iii) is guaranteed to work in polynomial space. Further, our procedure can be extended to compute all the answer sets still working in polynomial space. The experimental results of a prototypical implementation show that the approach can pay off sometimes by orders of magnitude when computing one solution, and it is competitive when computing all solutions.
Realizability of Concurrent Recursive Programs
, 2008
"... We define and study an automata model of concurrent recursive programs. An automaton consists of a finite number of pushdown systems running in parallel and communicating via shared actions. Actually, we combine multistack visibly pushdown automata and Zielonka’s asynchronous automata towards a mod ..."
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Cited by 3 (1 self)
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We define and study an automata model of concurrent recursive programs. An automaton consists of a finite number of pushdown systems running in parallel and communicating via shared actions. Actually, we combine multistack visibly pushdown automata and Zielonka’s asynchronous automata towards a model with an undecidable emptiness problem. However, a reasonable restriction allows us to lift Zielonka’s Theorem to this recursive setting and permits a logical characterization in terms of a suitable monadic secondorder logic. Building on results from Mazurkiewicz trace theory and recent work by La Torre, Madhusudan, and Parlato, we thus develop a framework for the specification, synthesis, and verification of concurrent recursive processes.
Unfolding Synthesis of Asynchronous Automata
 International Computer Science Symposium in Russia, CSR 2006. Available at http://www.cmi.univmrs.fr/˜morin/papers/CSR.pdf
"... Abstract. Zielonka’s theorem shows that each regular set of Mazurkiewicz traces can be implemented as a system of synchronized processes provided with some distributed control structure called an asynchronous automaton. This paper gives a new algorithm for the synthesis of a nondeterministic asynch ..."
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Abstract. Zielonka’s theorem shows that each regular set of Mazurkiewicz traces can be implemented as a system of synchronized processes provided with some distributed control structure called an asynchronous automaton. This paper gives a new algorithm for the synthesis of a nondeterministic asynchronous automaton from a regular Mazurkiewicz trace language. Our approach is based on an unfolding procedure that improves the complexity of Zielonka’s and Pighizzini’s techniques: Our construction is polynomial in terms of the number of states but still doubleexponential in the size of the alphabet. As opposed to Métivier’s work, our algorithm does not restrict to acyclic dependence alphabets.