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Algorithmic Verification of Asynchronous Programs
"... Asynchronous programming is a ubiquitous systems programming idiom to manage concurrent interactions with the environment. In this style, instead of waiting for timeconsuming operations to complete, the programmer makes a nonblocking call to the operation and posts a callback task to a task buffer ..."
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Cited by 21 (3 self)
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Asynchronous programming is a ubiquitous systems programming idiom to manage concurrent interactions with the environment. In this style, instead of waiting for timeconsuming operations to complete, the programmer makes a nonblocking call to the operation and posts a callback task to a task buffer that is executed later when the timeconsuming operation completes. A cooperative scheduler mediates the interaction by picking and executing callback tasks from the task buffer to completion (and these callbacks can post further callbacks to be executed later). Writing correct asynchronous programs is hard because the use of callbacks, while efficient, obscures program control flow. We provide a formal model underlying asynchronous programs and study verification problems for this model. We show that the safety verification problem for finitedata asynchronous programs is expspacecomplete. We show that liveness verification for finitedata asynchronous programs is decidable and polynomialtime equivalent to Petri Net reachability. Decidability is not obvious, since even if the data is finitestate, asynchronous programs constitute infinitestate transition systems: both the program stack and the task buffer of pending asynchronous calls can be potentially unbounded. Our main technical construction is a polynomialtime semanticspreserving reduction from asynchronous programs to Petri Nets and conversely. The reduction allows the use of algorithmic techniques on Petri Nets
Approximating Petri net reachability along contextfree traces
 In FSTTCS, volume 13 of LIPIcs
, 2011
"... ABSTRACT. We investigate the problem asking whether the intersection of a contextfree language (CFL) and a Petri net language (PNL) is empty. Our contribution to solve this longstanding problem which relates, for instance, to the reachability analysis of recursive programs over unbounded data doma ..."
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Cited by 6 (2 self)
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ABSTRACT. We investigate the problem asking whether the intersection of a contextfree language (CFL) and a Petri net language (PNL) is empty. Our contribution to solve this longstanding problem which relates, for instance, to the reachability analysis of recursive programs over unbounded data domain, is to identify a class of CFLs called the finiteindex CFLs for which the problem is decidable. The kindex approximation of a CFL can be obtained by discarding all the words that cannot be derived within a budget k on the number of occurrences of nonterminals. A finiteindex CFL is thus a CFL which coincides with its kindex approximation for some k. We decide whether the intersection of a finiteindex CFL and a PNL is empty by reducing it to the reachability problem of Petri nets with weak inhibitor arcs, a class of systems with infinitely many states for which reachability is known to be decidable. Conversely, we show that the reachability problem for a Petri net with weak inhibitor arcs reduces to the emptiness problem of a finiteindex CFL intersected with a PNL. 1
Lineartime modelchecking for multithreaded programs under scopebounding
 In Supratik Chakraborty and Madhavan Mukund, editors, ATVA, volume 7561 of Lecture Notes in Computer Science
, 2012
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Staged SelfAssembly and Polyomino ContextFree Grammars
"... Previous work by Demaine et al. (2012) developed a strong connection between smallest contextfree grammars and staged selfassembly systems for onedimensional strings and assemblies. We extend this work to twodimensional polyominoes and assemblies, comparing staged selfassembly systems to a nat ..."
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Previous work by Demaine et al. (2012) developed a strong connection between smallest contextfree grammars and staged selfassembly systems for onedimensional strings and assemblies. We extend this work to twodimensional polyominoes and assemblies, comparing staged selfassembly systems to a natural generalization of contextfree grammars we call polyomino contextfree grammars (PCFGs). We achieve nearly optimal bounds on the largest ratios of the smallest PCFG and staged selfassembly system for a given polyomino with n cells. For the ratio of PCFGs over assembly systems, we show that the smallest PCFG can be an Ω(n / log 3 n)factor larger than the smallest staged assembly system, even when restricted to square polyominoes. For the ratio of assembly systems over PCFGs, we show that the smallest staged assembly system is never more than a O(log n)factor larger than the smallest PCFG and is sometimes an Ω(log n / log log n)factor larger.
M.: Finite Automata for the Sub and Superword Closure of CFLs: Descriptional and Computational Complexity (extended version). arXiv:1410.2737
"... Abstract. We answer two open questions by (Gruber, Holzer, Kutrib, 2009) on the statecomplexity of representing sub or superword closures of contextfree grammars (CFGs): (1) We prove a (tight) upper bound of 2O(n) on the size of nondeterministic finite automata (NFAs) representing the subword clo ..."
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Abstract. We answer two open questions by (Gruber, Holzer, Kutrib, 2009) on the statecomplexity of representing sub or superword closures of contextfree grammars (CFGs): (1) We prove a (tight) upper bound of 2O(n) on the size of nondeterministic finite automata (NFAs) representing the subword closure of a CFG of size n. (2) We present a family of CFGs for which the minimal deterministic finite automata representing their subword closure matches the upperbound of 22 O(n) following from (1). Furthermore, we prove that the inequivalence problem for NFAs representing sub or superwordclosed languages is only NPcomplete as opposed to PSPACEcomplete for general NFAs. Finally, we extend our results into an approximation method to attack inequivalence problems for CFGs. 1
Gool. Earley parsing for 2D stochastic context free grammars
, 2013
"... In a companion paper, Bayesian Grammar Learning for Inverse Procedural Modeling, we have presented a novel approach of learning a specific variant of procedural grammars from data, namely 2D Attributed Stochastic Context Free Grammars, or 2DASCFGs. One of the essential parts of the grammar learning ..."
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In a companion paper, Bayesian Grammar Learning for Inverse Procedural Modeling, we have presented a novel approach of learning a specific variant of procedural grammars from data, namely 2D Attributed Stochastic Context Free Grammars, or 2DASCFGs. One of the essential parts of the grammar learning algorithm described therein is the Earley parser for 2DSCFGs. The purpose of this technical report is to provide the implementation details of this parser, illustrate the approach on simple examples, and discuss the improvements over the existing methods. 1.
Towards a Tight Integration of Syntactic Parsing with Semantic Disambiguation by means of Declarative Programming ∗
"... We propose and advocate the use of an advanced declarative programming paradigm – answer set programming – as a uniform platform for integrated approach towards syntaxsemantic processing in natural language. We illustrate that (a) the parsing technology based on answer set programming implementatio ..."
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We propose and advocate the use of an advanced declarative programming paradigm – answer set programming – as a uniform platform for integrated approach towards syntaxsemantic processing in natural language. We illustrate that (a) the parsing technology based on answer set programming implementation reaches performance sufficient for being a useful NLP tool, and (b) the proposed method for incorporating semantic information from FRAMENET into syntactic parsing may prove to be useful in allowing semanticbased disambiguation of syntactic structures. 1
Parsing Russian: a Hybrid Approach
"... We present an approach for natural language parsing in which dependency and constituency parses are acquired simultaneously. This leads to accurate parses represented in a specific way, richer than constituency or dependency tree. It also allows reducing parsing time complexity. Within the proposed ..."
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We present an approach for natural language parsing in which dependency and constituency parses are acquired simultaneously. This leads to accurate parses represented in a specific way, richer than constituency or dependency tree. It also allows reducing parsing time complexity. Within the proposed approach, we show how to treat some significant phenomena of the Russian language and also perform a brief evaluation of the parser implementation, known as DictaScope Syntax. 1
Inverting Dynamic Programming
"... Abstract. We suggest and discuss a formalization of Dynamic Programming. A methodological novelty consists in an explicit treatment (interpretation) of ascending Dynamic Programming as least fixpoint computation (according to KnasterTarski fixpoint theorem). This interpretation leads to a uniform ..."
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Abstract. We suggest and discuss a formalization of Dynamic Programming. A methodological novelty consists in an explicit treatment (interpretation) of ascending Dynamic Programming as least fixpoint computation (according to KnasterTarski fixpoint theorem). This interpretation leads to a uniform approach to classical optimization problems as well as to problems where optimality is not explicit (Cocke Younger Kasami parsing algorithm for example) and to problem of algorithm inversion (i.e. computing inverse function).