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111
Dynamic test input generation for database applications
 In ISSTA
, 2007
"... We describe an algorithm for automatic test input generation for database applications. Given a program in an imperative language that interacts with a database through API calls, our algorithm generates both input data for the program as well as suitable database records to systematically explore a ..."
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Cited by 77 (1 self)
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We describe an algorithm for automatic test input generation for database applications. Given a program in an imperative language that interacts with a database through API calls, our algorithm generates both input data for the program as well as suitable database records to systematically explore all paths of the program, including those paths whose execution depend on data returned by database queries. Our algorithm is based on concolic execution, where the program is run with concrete inputs and simultaneously also with symbolic inputs for both program variables as well as the database state. The symbolic constraints generated along a path enable us to derive new input values and new database records that can cause execution to hit uncovered paths. Simultaneously, the concrete execution helps to retain precision in the symbolic computations by allowing dynamic values to be used in the symbolic executor. This allows our algorithm, for example, to identify concrete SQL queries made by the program, even if these queries are built dynamically. The contributions of this paper are the following. We develop an algorithm that can track symbolic constraints across language boundaries and use those constraints in conjunction with a novel constraint solver to generate both program inputs and database state. We propose a constraint solver that can solve symbolic constraints consisting of both linear arithmetic constraints over variables as well as string constraints (string equality, disequality, as well as membership in regular languages). Finally, we provide an evaluation of the algorithm on a Java implementation of MediaWiki, a popular wiki package that interacts with a database backend.
Optimizing Büchi automata
, 2000
"... We describe a family of optimizations implemented in a translation from a linear temporal logic to Büchi automata. Such optimized automata can enhance the efficiency of explicit state model checking, as practiced in tools such as SPIN. Some of our optimizations are applicable to... ..."
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Cited by 75 (3 self)
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We describe a family of optimizations implemented in a translation from a linear temporal logic to Büchi automata. Such optimized automata can enhance the efficiency of explicit state model checking, as practiced in tools such as SPIN. Some of our optimizations are applicable to...
Expressive Languages for Path Queries over GraphStructured Data
, 2010
"... For many problems arising in the setting of graph querying (such as finding semantic associations in RDF graphs, exact and approximate pattern matching, sequence alignment, etc.), the power of standard languages such as the widely studied conjunctive regular path queries (CRPQs) is insufficient in a ..."
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Cited by 65 (17 self)
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For many problems arising in the setting of graph querying (such as finding semantic associations in RDF graphs, exact and approximate pattern matching, sequence alignment, etc.), the power of standard languages such as the widely studied conjunctive regular path queries (CRPQs) is insufficient in at least two ways. First, they cannot output paths and second, more crucially, they cannot express relations among paths. We thus propose a class of extended CRPQs, called ECRPQs, which add regular relations on tuples of paths, and allow path variables in the heads of queries. We provide several examples of their usefulness in querying graph structured data, and study their properties. We analyze query evaluation and representation of tuples of paths in the output by means of automata. We present a detailed analysis of data and combined complexity of queries, and consider restrictions that lower the complexity of ECRPQs to that of relational conjunctive queries. We study the containment problem, and look at further extensions with firstorder features, and with nonregular relations that express arithmetic properties of paths, based on the lengths and numbers of occurrences of labels.
The History and Status of the P versus NP Question
, 1992
"... this article, I have attempted to organize and describe this literature, including an occasional opinion about the most fruitful directions, but no technical details. In the first half of this century, work on the power of formal systems led to the formalization of the notion of algorithm and the re ..."
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Cited by 60 (1 self)
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this article, I have attempted to organize and describe this literature, including an occasional opinion about the most fruitful directions, but no technical details. In the first half of this century, work on the power of formal systems led to the formalization of the notion of algorithm and the realization that certain problems are algorithmically unsolvable. At around this time, forerunners of the programmable computing machine were beginning to appear. As mathematicians contemplated the practical capabilities and limitations of such devices, computational complexity theory emerged from the theory of algorithmic unsolvability. Early on, a particular type of computational task became evident, where one is seeking an object which lies
Space Complexity In Propositional Calculus
 SIAM JOURNAL OF COMPUTING
, 2002
"... We study space complexity in the framework of propositional proofs. We consider a natural model analogous to Turing machines with a readonly input tape and such popular propositional proof systems as resolution, polynomial calculus, and Frege systems. We propose two di#erent space measures, corresp ..."
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Cited by 49 (8 self)
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We study space complexity in the framework of propositional proofs. We consider a natural model analogous to Turing machines with a readonly input tape and such popular propositional proof systems as resolution, polynomial calculus, and Frege systems. We propose two di#erent space measures, corresponding to the maximal number of bits, and clauses/monomials that need to be kept in the memory simultaneously. We prove a number of lower and upper bounds in these models, as well as some structural results concerning the clause space for resolution and Frege systems.
Directional Type Checking of Logic Programs
 In Proceedings of the 1st International Static Analysis Symposium
, 1994
"... We present an algorithm for automatic type checking of logic programs with respect to directional types that describe both the structure of terms and the directionality of predicates. The type checking problem is reduced to a decidable problem on systems of inclusion constraints over set expressio ..."
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Cited by 48 (1 self)
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We present an algorithm for automatic type checking of logic programs with respect to directional types that describe both the structure of terms and the directionality of predicates. The type checking problem is reduced to a decidable problem on systems of inclusion constraints over set expressions. We discuss some properties of the reduction algorithm, complexity, and present a proof of correctness. 1 1 Introduction Most logic programming languages are untyped. In Prolog, for example, it is considered meaningful to apply any nary predicate to any ntuple of terms. However, it is generally accepted that static type checking has great advantages in detecting programming errors early and for generating efficient executable code. Motivated at least in part by the success of type systems for procedural and functional languages, there is currently considerable interest in finding appropriate definitions of type and welltyping for logic languages. This paper explores the type checki...
Improving Exhaustive Search Implies Superpolynomial Lower Bounds
, 2009
"... The P vs NP problem arose from the question of whether exhaustive search is necessary for problems with short verifiable solutions. We do not know if even a slight algorithmic improvement over exhaustive search is universally possible for all NP problems, and to date no major consequences have been ..."
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Cited by 40 (7 self)
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The P vs NP problem arose from the question of whether exhaustive search is necessary for problems with short verifiable solutions. We do not know if even a slight algorithmic improvement over exhaustive search is universally possible for all NP problems, and to date no major consequences have been derived from the assumption that an improvement exists. We show that there are natural NP and BPP problems for which minor algorithmic improvements over the trivial deterministic simulation already entail lower bounds such as NEXP ̸ ⊆ P/poly and LOGSPACE ̸ = NP. These results are especially interesting given that similar improvements have been found for many other hard problems. Optimistically, one might hope our results suggest a new path to lower bounds; pessimistically, they show that carrying out the seemingly modest program of finding slightly better algorithms for all search problems may be extremely difficult (if not impossible). We also prove unconditional superpolynomial timespace lower bounds for improving on exhaustive search: there is a problem verifiable with k(n) length witnesses in O(n a) time (for some a and some function k(n) ≤ n) that cannot be solved in k(n) c n a+o(1) time and k(n) c n o(1) space, for every c ≥ 1. While such problems can always be solved by exhaustive search in O(2 k(n) n a) time and O(k(n) + n a) space, we can prove a superpolynomial lower bound in the parameter k(n) when space usage is restricted.
Space Complexity of Random Formulae in Resolution
 In 16th IEEE Conference on Computational Complexity
, 2001
"... We study the space complexity of refuting unsatis able random k CNFs in the Resolution proof system. We prove that for any large enough , with high probability a random kCNF over n variables and n clauses requires resolution clause space of ), for any 0 < < 1=2. For constant , this ..."
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Cited by 40 (6 self)
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We study the space complexity of refuting unsatis able random k CNFs in the Resolution proof system. We prove that for any large enough , with high probability a random kCNF over n variables and n clauses requires resolution clause space of ), for any 0 < < 1=2. For constant , this gives us linear, optimal, lower bounds on the clause space.
Stochastic Plans for Robotic Manipulation
, 1990
"... Geometric uncertainty is unavoidable when programming robots for physical applications. We propose a stochastic framework for manipulation planning where plans are ranked on the basis of expected cost. That is, we express the desirability of states and actions with a cost function and describe uncer ..."
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Cited by 37 (9 self)
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Geometric uncertainty is unavoidable when programming robots for physical applications. We propose a stochastic framework for manipulation planning where plans are ranked on the basis of expected cost. That is, we express the desirability of states and actions with a cost function and describe uncertainty with probability distributions. We illustrate the approach with a new design for a programmable parts feeder, a mechanism that orients twodimensional parts using a sequence of openloop mechanical motions. We present a planning algorithm that accepts an nsided polygonal part as input and, in time O(n²), generates a stochastically optimal plan for orienting the part.
On the Power of Bounded Concurrency I: Finite Automata
 Journal of the ACM
, 1994
"... We investigate the descriptive succinctness of three fundamental notions for modeling concurrency: nondeterminism and pure parallelism, the two facets of alternation, and bounded cooperative concurrency, whereby a system configuration consists of a bounded number of cooperating states. Our results a ..."
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Cited by 36 (8 self)
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We investigate the descriptive succinctness of three fundamental notions for modeling concurrency: nondeterminism and pure parallelism, the two facets of alternation, and bounded cooperative concurrency, whereby a system configuration consists of a bounded number of cooperating states. Our results are couched in the general framework of finitestate automata, but hold for appropriate versions of most concurrent models of computation, such as Petri nets, statecharts or finitestate versions of concurrent programming languages. We exhibit exhaustive sets of upper and lower bounds on the relative succinctness of these features over * and ', establishing that: (1) Each of the three features represents an exponential saving in succinctness of the representa tion, in a manner that isindependent of the other two and additive with respect to them.