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51
A comparison of structural CSP decomposition methods
 Artificial Intelligence
, 2000
"... We compare tractable classes of constraint satisfaction problems (CSPs). We first give a uniform presentation of the major structural CSP decomposition methods. We then introduce a new class of tractable CSPs based on the concept of hypertree decomposition recently developed in Database Theory. We i ..."
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Cited by 178 (27 self)
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We compare tractable classes of constraint satisfaction problems (CSPs). We first give a uniform presentation of the major structural CSP decomposition methods. We then introduce a new class of tractable CSPs based on the concept of hypertree decomposition recently developed in Database Theory. We introduce a framework for comparing parametric decompositionbased methods according to tractability criteria and compare the most relevant methods. We show that the method of hypertree decomposition dominates the others in the case of general (nonbinary) CSPs.
ConjunctiveQuery Containment and Constraint Satisfaction
 Journal of Computer and System Sciences
, 1998
"... Conjunctivequery containment is recognized as a fundamental problem in database query evaluation and optimization. At the same time, constraint satisfaction is recognized as a fundamental problem in artificial intelligence. What do conjunctivequery containment and constraint satisfaction have in c ..."
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Cited by 168 (14 self)
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Conjunctivequery containment is recognized as a fundamental problem in database query evaluation and optimization. At the same time, constraint satisfaction is recognized as a fundamental problem in artificial intelligence. What do conjunctivequery containment and constraint satisfaction have in common? Our main conceptual contribution in this paper is to point out that, despite their very different formulation, conjunctivequery containment and constraint satisfaction are essentially the same problem. The reason is that they can be recast as the following fundamental algebraic problem: given two finite relational structures A and B, is there a homomorphism h : A ! B? As formulated above, the homomorphism problem is uniform in the sense that both relational structures A and B are part of the input. By fixing the structure B, one obtains the following nonuniform problem: given a finite relational structure A, is there a homomorphism h : A ! B? In general, nonuniform tractability results do not uniformize. Thus, it is natural to ask: which tractable cases of nonuniform tractability results for constraint satisfaction and conjunctivequery containment do uniformize? Our main technical contribution in this paper is to show that several cases of tractable nonuniform constraint satisfaction problems do indeed uniformize. We exhibit three nonuniform tractability results that uniformize and, thus, give rise to polynomialtime solvable cases of constraint satisfaction and conjunctivequery containment.
Constraint Satisfaction Problems And Finite Algebras
, 1999
"... Many natural combinatorial problems can be expressed as constraint satisfaction problems. This class of problems is known to be NPcomplete in general, but certain restrictions on the form of the constraints can ensure tractability. In this paper we show that any restricted set of constraint types c ..."
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Cited by 66 (9 self)
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Many natural combinatorial problems can be expressed as constraint satisfaction problems. This class of problems is known to be NPcomplete in general, but certain restrictions on the form of the constraints can ensure tractability. In this paper we show that any restricted set of constraint types can be associated with a finite universal algebra. We explore how the computational complexity of a restricted constraint satisfaction problem is connected to properties of the corresponding algebra. For this, we introduce a notion of `tractable algebra' and study how the tractability of an algebra relates to the tractability of its smaller derived algebras, including its subalgebras and homomorphic images. This allows us to significantly reduce the types of algebras which need to be investigated. Using these results we exhibit a common structural property of all known intractable constraint satisfaction problems. Finally, we classify all finite strictly simple surjective algebras wit...
Hypertree decompositions: A survey
 In: MFCS ’01: Proceedings of the 26th International Symposium on Mathematical Foundations of Computer Science
, 2001
"... Abstract. This paper surveys recent results related to the concept of hypertree decomposition and the associated notion of hypertree width. A hypertree decomposition of a hypergraph (similar to a tree decomposition of a graph) is a suitable clustering of its hyperedges yielding a tree or a forest. I ..."
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Cited by 39 (5 self)
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Abstract. This paper surveys recent results related to the concept of hypertree decomposition and the associated notion of hypertree width. A hypertree decomposition of a hypergraph (similar to a tree decomposition of a graph) is a suitable clustering of its hyperedges yielding a tree or a forest. Important NP hard problems become tractable if restricted to instances whose associated hypergraphs are of bounded hypertree width. We also review a number of complexity results on problems whose structure is described by acyclic or nearly acyclic hypergraphs. 1
Web service discovery based on behavior signatures
 In Proc. of SCC 2005
, 2005
"... Web service discovery is a key problem as the number of services is expected to increase dramatically. Service discovery at the present time is based primarily on keywords, or interfaces of web services through the use of ontology. We argue that “behavior signatures ” as operational level descriptio ..."
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Cited by 32 (2 self)
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Web service discovery is a key problem as the number of services is expected to increase dramatically. Service discovery at the present time is based primarily on keywords, or interfaces of web services through the use of ontology. We argue that “behavior signatures ” as operational level description should play an important role in the service discovery process. In this paper, we propose a new behavior model for web services using automata and logic formalisms. Roughly, the model associates messages with activities and adopts the IOPR model in OWLS to describe activities. A new query language is developed to express temporal and semantic properties on service behaviors. Query evaluation algorithms are developed; in particular, an optimization approach using REtree and heuristics is shown to improve the performance. Specifically, experimental results show that the use of REtree reduces query evaluation time by an order of magnitude and with heuristics it enhances the performance by two orders of magnitude. This is clearly an encouraging starting point. 1
Surveillance in virtual reality: System design and multicamera control
 In CVPR, 2007. 3
"... This paper advocates a Virtual Vision paradigm and demonstrates its usefulness in camera sensor network research. Virtual vision prescribes the use of a visually and behaviorally realistic virtual environment simulator in the design and evaluation of surveillance systems. Impediments to deploying an ..."
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Cited by 23 (1 self)
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This paper advocates a Virtual Vision paradigm and demonstrates its usefulness in camera sensor network research. Virtual vision prescribes the use of a visually and behaviorally realistic virtual environment simulator in the design and evaluation of surveillance systems. Impediments to deploying and experimenting with appropriately complex camera networks makes virtual vision an attractive alternative for many vision researchers who are motivated to investigate high level multicamera control issues within such networks. In particular, we present two prototype surveillance systems comprising passive and active pan/tilt/zoom cameras. We deploy these systems in a virtual train station environment populated by autonomous, lifelike virtual pedestrians. The easily reconfigurable virtual cameras situated throughout this environment generate synthetic video feeds that emulate those acquired by real surveillance cameras monitoring extensive public spaces. Our novel multicamera control strategies enable the cameras to collaborate in persistently observing pedestrians of interest that move across their fields of view and in capturing closeup videos of pedestrians as they travel through designated areas. The sensor networks support taskdependent camera node selection and aggregation through local decisionmaking and internode communication. Our approach to multicamera control is robust to node failures and message loss. 1.
FixedParameter Complexity in AI and Nonmonotonic Reasoning
, 1999
"... This paper studies the fixedparameter complexity of various problems in AI and nonmonotonic reasoning. We show that a number of relevant parameterized problems in these areas are fixedparameter tractable. Among these problems are constraint satisfaction problems with bounded treewidth and fixed ..."
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Cited by 23 (1 self)
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This paper studies the fixedparameter complexity of various problems in AI and nonmonotonic reasoning. We show that a number of relevant parameterized problems in these areas are fixedparameter tractable. Among these problems are constraint satisfaction problems with bounded treewidth and fixed domain, restricted satisfiability problems, propositional logic programming under the stable model semantics where the parameter is the dimension of a feedback vertex set of the program's dependency graph, and circumscriptive inference from a positive kCNF restricted to models of bounded size. We also show that circumscriptive inference from a general propositional theory, when the attention is restricted to models of bounded size, is fixedparameter intractable and is actually complete for a novel fixedparameter complexity class. Keywords: Complexity, Fixedparameter Tractability, Nonmonotonic Reasoning, Constraint Satisfaction, Prime Implicants, Logic Programming, Stable Models, C...
Smart camera networks in virtual reality
 Proceedings of the IEEE
, 2008
"... This paper presents smart camera network research in the context of a unique new synthesis of advanced computer graphics and vision simulation technologies. We design and experiment with simulated camera networks within visually and behaviorally realistic virtual environments. Specifically, we demon ..."
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Cited by 22 (10 self)
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This paper presents smart camera network research in the context of a unique new synthesis of advanced computer graphics and vision simulation technologies. We design and experiment with simulated camera networks within visually and behaviorally realistic virtual environments. Specifically, we demonstrate a smart camera network comprising static and active simulated video surveillance cameras that provides perceptive coverage of a large virtual public space, a train station populated by autonomously selfanimating virtual pedestrians. In the context of human surveillance, we propose a camera network control strategy that enables a collection of smart cameras to provide perceptive scene coverage and perform persistent surveillance with minimal intervention. Our novel control strategy naturally addresses camera aggregation and camera handoff, it does not require camera calibration, a detailed world model, or a central controller, and it is robust against camera failures and communication errors.
Constraint Satisfaction and Database Theory: a Tutorial
 19th ACM Symposium on Principles of Database Systems
, 2000
"... A large class of problems in AI and other areas of computer science can be viewed as constraintsatisfaction problems. This includes problems in machine vision, belief maintenance, scheduling, temporal reasoning, type reconstruction, graph theory, and satisability. In general, the constraint satisfa ..."
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Cited by 21 (0 self)
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A large class of problems in AI and other areas of computer science can be viewed as constraintsatisfaction problems. This includes problems in machine vision, belief maintenance, scheduling, temporal reasoning, type reconstruction, graph theory, and satisability. In general, the constraint satisfactionproblem is NPcomplete, so searching for tractable cases is an active research area. It turns out that constraint satisfaction has an intimate connection with database theory: constraintsatisfaction problems can be recast as database problems and database problems can be recast as constraintsatisfaction problems. In this tutorial, I will cover the fundamentals of constraints saisfaction and describe its intimate relationship with database theory from various perspectives. 1 Introduction Since the early 1970s, researchers in articial intelligence have investigated a class of combinatorial problems that became known as constraintsatisfaction problems (CSP). The input to such a pro...
Tractable Constraints Closed Under A Binary Operation
 Oxford University
, 2000
"... Many combinatorial search problems can be expressed as instances of the "constraint satisfaction problem" (CSP). This class of problems is known to be NPcomplete in general, so to ensure tractability it is natural to consider restricted subproblems in which the constraints have certain sp ..."
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Cited by 15 (7 self)
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Many combinatorial search problems can be expressed as instances of the "constraint satisfaction problem" (CSP). This class of problems is known to be NPcomplete in general, so to ensure tractability it is natural to consider restricted subproblems in which the constraints have certain specified forms. The algebraic approach to the CSP maintains that certain algebraic invariance properties of constraints can be used to determine the complexity of these restricted problems.