Datasets:

allenai

/

multixscience_dense_max

like 1

{ "cite_N": [ "@cite_0", "@cite_5", "@cite_18" ], "mid": [ "2163593765", "2104380208", "" ], "abstract": [ "In modern computers, the floating point unit is the part of the processor delivering the highest computing power and getting most attention from the design team. Performance of any multiple precision application will be dramatically enhanced by adequate use of floating point expansions. We present three multiplication algorithms, faster and more integrated than the stepwise algorithm proposed earlier. We have tested these novel algorithms on an application that computes the determinant of a matrix. In the absence of overflow or underflow, the process is error free and possibly more efficient than its integer based counterpart.", "A quad-double number is an unevaluated sum of four IEEE double precision numbers, capable of representing at least 212 bits of significand. We present the algorithms for various arithmetic operations (including the four basic operations and various algebraic and transcendental operations) on quad-double numbers. The performance of the algorithms, implemented in C++, is also presented.", "" ] }

{ "cite_N": [ "@cite_14" ], "mid": [ "69766967" ], "abstract": [ "There is a growing demand for high precision texture formats fed by the increasing number of textures per pixel and multi-pass algorithms in dynamic texturing and visualization. Therefore support for wider data formats in graphics hardware is evolving. The existing functionality of current graphics cards, however, can already be used to provide higher precision textures. This paper shows how to emulate a 16 bit precise signed format by use of RGBA8 textures and existing shader and register operations. Thereby a 16 bit number is stored in two unsigned 8 bit color channels. The focus lies on a 16 bit signed number format which generalizes existing 8 bit formats allowing lossless format expansions, and which has an exact representation of 1, 0 and allowing stable long-lasting dynamic texture updates. Implementations of basic arithmetic operations and dependent texture loop-ups in this format are presented and example algorithms dealing with 16 bit precise dynamic updates of displacement maps, normal textures and filters demonstrate some of the resulting application areas." ] }

{ "cite_N": [ "@cite_4" ], "mid": [ "1967088292" ], "abstract": [ "In this paper we give a polynomial-time quantum algorithm for computing orders of solvable groups. Several other problems, such as testing membership in solvable groups, testing equality of subgroups in a given solvable group, and testing normality of a subgroup in a given solvable group, reduce to computing orders of solvable groups and therefore admit polynomial-time quantum algorithms as well. Our algorithm works in the setting of black-box groups, wherein none of these problems have polynomial-time classical algorithms. As an important byproduct, our algorithm is able to produce a pure quantum state that is uniform over the elements in any chosen subgroup of a solvable group, which yields a natural way to apply existing quantum algorithms to factor groups of solvable groups." ] }

{ "cite_N": [ "@cite_18", "@cite_4", "@cite_21", "@cite_2", "@cite_25", "@cite_11" ], "mid": [ "", "2027433115", "2133454221", "1593492645", "1828504193", "" ], "abstract": [ "", "In genetic programming (GP), learning problems can be classified broadly into two types: those using data sets, as in supervised learning, and those using an environment as a source of feedback. An increasing amount of research has concentrated on the robustness or generalization ability of the programs evolved using GP. While some of the researchers report on the brittleness of the solutions evolved, others proposed methods of promoting robustness generalization. It is important that these methods are not ad hoc and are applicable to other experimental setups. In this paper, learning concepts from traditional machine learning and a brief review of research on generalization in GP are presented. The paper also identifies problems with brittleness of solutions produced by GP and suggests a method for promoting robustness generalization of the solutions in simulating learning behaviors using GP.", "EC-based supervised learning has been demonstrated to be an effective approach to forming predictive models in genomics, spectral interpretation, and other problems in modern biology. Longer-established methods such as PLS and ANN are also often successful. In supervised learning, overtraining is always a potential problem. The literature reports numerous methods of validating predictive models in order to avoid overtraining. Some of these approaches can be applied to EC-based methods of supervised learning, though the characteristics of EC learning are different from those obtained with PLS and ANN and selecting a suitably general model can be more difficult. This paper reviews the issues and various approaches, illustrating salient points with examples taken from applications in bioinformatics.", "This paper applies the evolution of GP teams to different classification and regression problems and compares different methods for combining the outputs of the team programs. These include hybrid approaches where (1) a neural network is used to optimize the weights of programs in a team for a common decision and (2) a realnumbered vector (the representation of evolution strategies) of weights is evolved with each term in parallel. The cooperative team approach results in an improved training and generalization performance compared to the standard GP method. The higher computational overhead of team evolution is counteracted by using a fast variant of linear GP.", "Many evolutionary computation search spaces require fitness assessment through the sampling of and generalization over a large set of possible cases as input. Such spaces seem particularly apropos to Genetic Programming, which notionally searches for computer algorithms and functions. Most existing research in this area uses ad-hoc approaches to the sampling task, guided more by intuition than understanding. In this initial investigation, we compare six approaches to sampling large training case sets in the context of genetic programming representations. These approaches include fixed and random samples, and adaptive methods such as coevolution or fitness sharing. Our results suggest that certain domain features may lead to the preference of one approach to generalization over others. In particular, coevolution methods are strongly domain-dependent. We conclude the paper with suggestions for further investigations to shed more light onto how one might adjust fitness assessment to make various methods more effective.", "" ] }

{ "cite_N": [ "@cite_22", "@cite_1", "@cite_19", "@cite_23", "@cite_5", "@cite_15", "@cite_13", "@cite_12", "@cite_17" ], "mid": [ "2155582960", "2139470281", "1591505907", "", "1592596255", "83216595", "1951785234", "1500215390", "1761022139" ], "abstract": [ "Genetic programming is distinguished from other evolutionary algorithms in that it uses tree representations of variable size instead of linear strings of fixed length. The flexible representation scheme is very important because it allows the underlying structure of the data to be discovered automatically. One primary difficulty, however, is that the solutions may grow too big without any improvement of their generalization ability. In this article we investigate the fundamental relationship between the performance and complexity of the evolved structures. The essence of the parsimony problem is demonstrated empirically by analyzing error landscapes of programs evolved for neural network synthesis. We consider genetic programming as a statistical inference problem and apply the Bayesian model-comparison framework to introduce a class of fitness functions with error and complexity terms. An adaptive learning method is then presented that automatically balances the model-complexity factor to evolve parsimonious programs without losing the diversity of the population needed for achieving the desired training accuracy. The effectiveness of this approach is empirically shown on the induction of sigma-pi neural networks for solving a real-world medical diagnosis problem as well as benchmark tasks.", "Genetic Programming (GP) uses variable size representations as programs. Size becomes an important and interesting emergent property of the structures evolved by GP. The size of programs can be both a controlling and a controlled factor in GP search. Size influences the efficiency of the search process and is related to the generality of solutions. This paper analyzes the size and generality issues in standard GP and GP using subroutines and addresses the question whether such an analysis can help control the search process. We relate the size, generalization and modularity issues for programs evolved to control an agent in a dynamic and non-deterministic environment, as exemplified by the Pac-Man game.", "The rapid growth of program code is an important problem in genetic programming systems. In the present paper we investigate a selection scheme based on multiobjective optimization. Since we want to obtain accurate and small solutions, we reformulate this problem as multiobjective optimization. We show that selection based on the Pareto nondomination criterion reduces code growth and processing time without significant loss of solution accuracy.", "", "", "", "A common data mining heuristic is, \"when choosing between models with the same training error, less complex models should be preferred as they perform better on unseen data\". This heuristic may not always hold. In genetic programming a preference for less complex models is implemented as: (i) placing a limit on the size of the evolved program; (ii) penalizing more complex individuals, or both. The paper presents a GP-variant with no limit on the complexity of the evolved program that generates highly accurate models on a common dataset.", "", "Many KDD systems incorporate an implicit or explicit preference for simpler models, but this use of “Occam‘s razor” has been strongly criticized by several authors (e.g., Schaffer, 1993s Webb, 1996). This controversy arises partly because Occam‘s razor has been interpreted in two quite different ways. The first interpretation (simplicity is a goal in itself) is essentially correct, but is at heart a preference for more comprehensible models. The second interpretation (simplicity leads to greater accuracy) is much more problematic. A critical review of the theoretical arguments for and against it shows that it is unfounded as a universal principle, and demonstrably false. A review of empirical evidence shows that it also fails as a practical heuristic. This article argues that its continued use in KDD risks causing significant opportunities to be missed, and should therefore be restricted to the comparatively few applications where it is appropriate. The article proposes and reviews the use of domain constraints as an alternative for avoiding overfitting, and examines possible methods for handling the accuracy–comprehensibility trade-off." ] }

{ "cite_N": [ "@cite_5", "@cite_8" ], "mid": [ "80590317", "2027993053" ], "abstract": [ "Dept. of Computer Science, K.U.LeuvenCelestijnenlaan 200A, B-3001 Heverlee, BelgiumE-mail: pelov,marcd,maurice @cs.kuleuven.ac.beAbstract. We define a translation of aggregate programs to normal lo-gic programs which preserves the set of partial stable models. We thendefine the classes of definite and stratified aggregate programs and showthat the translation of such programs are, respectively, definite and strat-ified logic programs. Consequently these two classes of programs havea single partial stable model which is two-valued and is also the well-founded model. Our definition of stratification is more general than theexisting one and covers a strictly larger class of programs.", "The aim of this paper is to extend theConstructive Negation technique to the case ofCLP(SeT), a Constraint Logic Programming (CLP) language based on hereditarily (and hybrid) finite sets. The challenging aspects of the problem originate from the fact that the structure on whichCLP(SeT) is based is notadmissible closed, and this does not allow to reuse the results presented in the literature concerning the relationships betweenCLP and constructive negation." ] }

{ "cite_N": [ "@cite_5", "@cite_11", "@cite_2" ], "mid": [ "80590317", "1520574003", "125332145" ], "abstract": [ "Dept. of Computer Science, K.U.LeuvenCelestijnenlaan 200A, B-3001 Heverlee, BelgiumE-mail: pelov,marcd,maurice @cs.kuleuven.ac.beAbstract. We define a translation of aggregate programs to normal lo-gic programs which preserves the set of partial stable models. We thendefine the classes of definite and stratified aggregate programs and showthat the translation of such programs are, respectively, definite and strat-ified logic programs. Consequently these two classes of programs havea single partial stable model which is two-valued and is also the well-founded model. Our definition of stratification is more general than theexisting one and covers a strictly larger class of programs.", "We introduce a family of partial stable model semantics for logic programs with arbitrary aggregate relations. The semantics are parametrized by the interpretation of aggregate relations in three-valued logic. Any semantics in this family satisfies two important properties: (i) it extends the partial stable semantics for normal logic programs and (ii) total stable models are always minimal. We also give a specific instance of the semantics and show that it has several attractive features.", "" ] }

{ "cite_N": [ "@cite_5" ], "mid": [ "80590317" ], "abstract": [ "Dept. of Computer Science, K.U.LeuvenCelestijnenlaan 200A, B-3001 Heverlee, BelgiumE-mail: pelov,marcd,maurice @cs.kuleuven.ac.beAbstract. We define a translation of aggregate programs to normal lo-gic programs which preserves the set of partial stable models. We thendefine the classes of definite and stratified aggregate programs and showthat the translation of such programs are, respectively, definite and strat-ified logic programs. Consequently these two classes of programs havea single partial stable model which is two-valued and is also the well-founded model. Our definition of stratification is more general than theexisting one and covers a strictly larger class of programs." ] }

{ "cite_N": [ "@cite_5" ], "mid": [ "80590317" ], "abstract": [ "Dept. of Computer Science, K.U.LeuvenCelestijnenlaan 200A, B-3001 Heverlee, BelgiumE-mail: pelov,marcd,maurice @cs.kuleuven.ac.beAbstract. We define a translation of aggregate programs to normal lo-gic programs which preserves the set of partial stable models. We thendefine the classes of definite and stratified aggregate programs and showthat the translation of such programs are, respectively, definite and strat-ified logic programs. Consequently these two classes of programs havea single partial stable model which is two-valued and is also the well-founded model. Our definition of stratification is more general than theexisting one and covers a strictly larger class of programs." ] }

{ "cite_N": [ "@cite_3", "@cite_6", "@cite_2" ], "mid": [ "1600965014", "2066859698", "2043811931" ], "abstract": [ "This paper shows how system-specific static analysis can find security errors that violate rules such as \"integers from untrusted sources must be sanitized before use\" and \"do not dereference user-supplied pointers.\" In our approach, programmers write system-specific extensions that are linked into the compiler and check their code for errors. We demonstrate the approach's effectiveness by using it to find over 100 security errors in Linux and OpenBSD, over 50 of which have led to kernel patches. An unusual feature of our approach is the use of methods to automatically detect when we miss code actions that should be checked.", "Systems software such as OS kernels, embedded systems, and libraries must obey many rules for both correctness and performance. Common examples include \"accesses to variable A must be guarded by lock B,\" \"system calls must check user pointers for validity before using them,\" and \"message handlers should free their buffers as quickly as possible to allow greater parallelism.\" Unfortunately, adherence to these rules is largely unchecked. This paper attacks this problem by showing how system implementors can use meta-level compilation (MC) to write simple, system-specific compiler extensions that automatically check their code for rule violations. By melding domain-specific knowledge with the automatic machinery of compilers, MC brings the benefits of language-level checking and optimizing to the higher, \"meta\" level of the systems implemented in these languages. This paper demonstrates the effectiveness of the MC approach by applying it to four complex, real systems: Linux, OpenBSD, the Xok exokernel, and the FLASH machine's embedded software. MC extensions found roughly 500 errors in these systems and led to numerous kernel patches. Most extensions were less than a hundred lines of code and written by implementors who had a limited understanding of the systems checked.", "A major obstacle to finding program errors in a real system is knowing what correctness rules the system must obey. These rules are often undocumented or specified in an ad hoc manner. This paper demonstrates techniques that automatically extract such checking information from the source code itself, rather than the programmer, thereby avoiding the need for a priori knowledge of system rules.The cornerstone of our approach is inferring programmer \"beliefs\" that we then cross-check for contradictions. Beliefs are facts implied by code: a dereference of a pointer, p, implies a belief that p is non-null, a call to \"unlock(1)\" implies that 1 was locked, etc. For beliefs we know the programmer must hold, such as the pointer dereference above, we immediately flag contradictions as errors. For beliefs that the programmer may hold, we can assume these beliefs hold and use a statistical analysis to rank the resulting errors from most to least likely. For example, a call to \"spin_lock\" followed once by a call to \"spin_unlock\" implies that the programmer may have paired these calls by coincidence. If the pairing happens 999 out of 1000 times, though, then it is probably a valid belief and the sole deviation a probable error. The key feature of this approach is that it requires no a priori knowledge of truth: if two beliefs contradict, we know that one is an error without knowing what the correct belief is.Conceptually, our checkers extract beliefs by tailoring rule \"templates\" to a system --- for example, finding all functions that fit the rule template \"a must be paired with b.\" We have developed six checkers that follow this conceptual framework. They find hundreds of bugs in real systems such as Linux and OpenBSD. From our experience, they give a dramatic reduction in the manual effort needed to check a large system. Compared to our previous work [9], these template checkers find ten to one hundred times more rule instances and derive properties we found impractical to specify manually." ] }

{ "cite_N": [ "@cite_8" ], "mid": [ "2124877509" ], "abstract": [ "This article shows how to use model checking to find serious errors in file systems. Model checking is a formal verification technique tuned for finding corner-case errors by comprehensively exploring the state spaces defined by a system. File systems have two dynamics that make them attractive for such an approach. First, their errors are some of the most serious, since they can destroy persistent data and lead to unrecoverable corruption. Second, traditional testing needs an impractical, exponential number of test cases to check that the system will recover if it crashes at any point during execution. Model checking employs a variety of state-reducing techniques that allow it to explore such vast state spaces efficiently.We built a system, FiSC, for model checking file systems. We applied it to four widely-used, heavily-tested file systems: ext3, JFS, ReiserFS and XFS. We found serious bugs in all of them, 33 in total. Most have led to patches within a day of diagnosis. For each file system, FiSC found demonstrable events leading to the unrecoverable destruction of metadata and entire directories, including the file system root directory “ ”." ] }

{ "cite_N": [ "@cite_0" ], "mid": [ "1499241274" ], "abstract": [ "Strictly limiting the lifetime (i.e. propagation and duration of exposure) of sensitive data (e.g. passwords) is an important and well accepted practice in secure software development. Unfortunately, there are no current methods available for easily analyzing data lifetime, and very little information available on the quality of today's software with respect to data lifetime. We describe a system we have developed for analyzing sensitive data lifetime through whole system simulation called TaintBochs. TaintBochs tracks sensitive data by \"tainting\" it at the hardware level. Tainting information is then propagated across operating system, language, and application boundaries, permitting analysis of sensitive data handling at a whole system level. We have used TaintBochs to analyze sensitive data handling in several large, real world applications. Among these were Mozilla, Apache, and Perl, which are used to process millions of passwords, credit card numbers, etc. on a daily basis. Our investigation reveals that these applications and the components they rely upon take virtually no measures to limit the lifetime of sensitive data they handle, leaving passwords and other sensitive data scattered throughout user and kernel memory. We show how a few simple and practical changes can greatly reduce sensitive data lifetime in these applications." ] }

{ "cite_N": [ "@cite_11" ], "mid": [ "2102970979" ], "abstract": [ "Software vulnerabilities have had a devastating effect on the Internet. Worms such as CodeRed and Slammer can compromise hundreds of thousands of hosts within hours or even minutes, and cause millions of dollars of damage [26, 43]. To successfully combat these fast automatic Internet attacks, we need fast automatic attack detection and filtering mechanisms. In this paper we propose dynamic taint analysis for automatic detection of overwrite attacks, which include most types of exploits. This approach does not need source code or special compilation for the monitored program, and hence works on commodity software. To demonstrate this idea, we have implemented TaintCheck, a mechanism that can perform dynamic taint analysis by performing binary rewriting at run time. We show that TaintCheck reliably detects most types of exploits. We found that TaintCheck produced no false positives for any of the many different programs that we tested. Further, we describe how TaintCheck could improve automatic signature generation in" ] }

{ "cite_N": [ "@cite_6", "@cite_8" ], "mid": [ "2161981474", "2156192134" ], "abstract": [ "In this paper we study the lengths of the routes in ad hoc networks. We propose a simplified theoretical model having as objective to estimate the path length for the routing protocols that are using flooding during their path discovery phase. We show how to evaluate the average gain in the hop number that one can obtain by using a simple reduction strategy. We prove the gain to be linear under very general conditions and show how it can be computed practically.", "The probability distribution is found for the link distance between two randomly positioned mobile radios in a wireless network for two representative deployment scenarios: (1) the mobile locations are uniformly distributed over a rectangular area and (2) the x and y coordinates of the mobile locations have Gaussian distributions. It is shown that the shapes of the link distance distributions for these scenarios are very similar when the width of the rectangular area in the first scenario is taken to be about three times the standard deviation of the location distribution in the second scenario. Thus the choice of mobile location distribution is not critical, but can be selected for the convenience of other aspects of the analysis or simulation of the mobile system." ] }

{ "cite_N": [ "@cite_0" ], "mid": [ "2126003739" ], "abstract": [ "Since ad hoc and sensor networks can be composed of a very large number of devices, the scalability of network protocols is a major design concern. Furthermore, network protocols must be designed to prolong the battery lifetime of the devices. However, most existing routing techniques for ad hoc networks are known not to scale well. On the other hand, the so-called geographical routing algorithms are known to be scalable but their energy efficiency has never been extensively and comparatively studied. In a geographical routing algorithm, data packets are forwarded by a node to its neighbor based on their respective positions. The neighborhood of each node is constituted by the nodes that lie within a certain radio range. Thus, from the perspective of a node forwarding a packet, the next hop depends on the width of the neighborhood it perceives. The analytical framework proposed in this paper allows to analyze the relationship between the energy efficiency of the routing tasks and the extension of the range of the topology knowledge for each node. A wider topology knowledge may improve the energy efficiency of the routing tasks but increases the cost of topology information due to signaling packets needed to acquire this information. The problem of determining the optimal topology knowledge range for each node to make energy efficient geographical routing decisions is tackled by integer linear programming. It is shown that the problem is intrinsically localized, i.e., a limited topology knowledge is sufficient to make energy efficient forwarding decisions. The leading forwarding rules for geographical routing are compared in this framework, and the energy efficiency of each of them is studied. Moreover, a new forwarding scheme, partial topology knowledge forwarding (PTKF), is introduced, and shown to outperform other existing schemes in typical application scenarios. A probe-based distributed protocol for knowledge range adjustment (PRADA) is finally introduced that allows each node to efficiently select online its topology knowledge range. PRADA is shown to rapidly converge to a near-optimal solution." ] }

{ "cite_N": [ "@cite_13", "@cite_9", "@cite_1" ], "mid": [ "1561598073", "2112169033", "2120361596" ], "abstract": [ "The task of moving data (i.e., the routing problem) in large-scale sensor networks has to contend with several obstacles, including severe power constraints at each node and temporary, but random, failures of nodes, rendering routing schemes designed for traditional communication networks ineffective. We consider the open problem of finding optimum routes between any fixed source-destination pair in a large-scale network, such that the communication load (i.e., the required power) is distributed among all the nodes, the overall latency is minimized, and the algorithm is decentralized and robust. A recent work addressed this problem in the context of a grid topology and showed how to obtain load-balanced routing, but transmissions are restricted to be among near-neighbors and the overall latency grows linearly with the number of nodes. We show how one can route messages between source and destination nodes along random small-world topologies using a decentralized algorithm. Specifically, nodes make connections independently (based only on the source and destination information in the packets), according to a distribution that guarantees an average latency of O(log sup 2 (N)), while preventing hotspot regions by providing an almost uniform distribution of traffic load over all nodes. Surprisingly, the randomized nature of the network structure keeps the average per-node power consumption almost the same as in the case of a grid topology (i.e., local transmissions), while providing an exponential reduction in latency, resulting in a highly fault-tolerant and stable design capable of working in very dynamic environments.", "The upcoming gigabit-per-second high-speed networks are expected to support a wide range of communication-intensive real-time multimedia applications. The requirement for timely delivery of digitized audio-visual information raises new challenges for next-generation integrated services broadband networks. One of the key issues is QoS routing. It selects network routes with sufficient resources for the requested QoS parameters. The goal of routing solutions is twofold: (1) satisfying the QoS requirements for every admitted connection, and (2) achieving global efficiency in resource utilization. Many unicast multicast QoS routing algorithms have been published, and they work with a variety of QoS requirements and resource constraints. Overall, they can be partitioned into three broad classes: (1) source routing, (2) distributed routing, and (3) hierarchical routing algorithms. We give an overview of the QoS routing problem as well as the existing solutions. We present the strengths and weaknesses of different routing strategies, and outline the challenges. We also discuss the basic algorithms in each class, classify and compare them, and point out possible future directions in the QoS routing area.", "We consider a routing problem in the context of large scale networks with uncontrolled dynamics. A case of uncontrolled dynamics that has been studied extensively is that of mobile nodes, as this is typically the case in cellular and mobile ad-hoc networks. In this paper however we study routing in the presence of a different type of dynamics: nodes do not move, but instead switch between active and inactive states at random times. Our interest in this case is motivated by the behavior of sensor nodes powered by renewable sources, such as solar cells or ambient vibrations. In this paper we formalize the corresponding routing problem as a problem of constructing suitably constrained random walks on random dynamic graphs. We argue that these random walks should be designed so that their resulting invariant distribution achieves a certain load balancing property, and we give simple distributed algorithms to compute the local parameters for the random walks that achieve the sought behavior. A truly novel feature of our formulation is that the algorithms we obtain are able to route messages along all possible routes between a source and a destination node, without performing explicit route discovery repair computations, and without maintaining explicit state information about available routes at the nodes. To the best of our knowledge, these are the first algorithms that achieve true multipath routing (in a statistical sense), at the complexity of simple stateless operations." ] }

{ "cite_N": [ "@cite_14", "@cite_7", "@cite_1", "@cite_6", "@cite_0", "@cite_2", "@cite_12" ], "mid": [ "2101982583", "", "2165004589", "2063289366", "2061177108", "2169958062", "1525038591" ], "abstract": [ "We consider the problem of decentralized detection under constraints on the number of bits that can be transmitted by each sensor. In contrast to most previous work, in which the joint distribution of sensor observations is assumed to be known, we address the problem when only a set of empirical samples is available. We propose a novel algorithm using the framework of empirical risk minimization and marginalized kernels, and analyze its computational and statistical properties both theoretically and empirically. We provide an efficient implementation of the algorithm, and demonstrate its performance on both simulated and real data sets.", "", "We present distributed regression, an efficient and general framework for in-network modeling of sensor data. In this framework, the nodes of the sensor network collaborate to optimally fit a global function to each of their local measurements. The algorithm is based upon kernel linear regression, where the model takes the form of a weighted sum of local basis functions; this provides an expressive yet tractable class of models for sensor network data. Rather than transmitting data to one another or outside the network, nodes communicate constraints on the model parameters, drastically reducing the communication required. After the algorithm is run, each node can answer queries for its local region, or the nodes can efficiently transmit the parameters of the model to a user outside the network. We present an evaluation of the algorithm based upon data from a 48-node sensor network deployment at the Intel Research - Berkeley Lab, demonstrating that our distributed algorithm converges to the optimal solution at a fast rate and is very robust to packet losses.", "We introduce a new formal model in which a learning algorithm must combine a collection of potentially poor but statistically independent hypothesis functions in order to approximate an unknown target function arbitrarily well. Our motivation includes the question of how to make optimal use of multiple independent runs of a mediocre learning algorithm, as well as settings in which the many hypotheses are obtained by a distributed population of identical learning agents.", "Motivated by sensor networks and other distributed settings, several models for distributed learning are presented. The models differ from classical works in statistical pattern recognition by allocating observations of an independent and identically distributed (i.i.d.) sampling process among members of a network of simple learning agents. The agents are limited in their ability to communicate to a central fusion center and thus, the amount of information available for use in classification or regression is constrained. For several basic communication models in both the binary classification and regression frameworks, we question the existence of agent decision rules and fusion rules that result in a universally consistent ensemble; the answers to this question present new issues to consider with regard to universal consistency. This paper addresses the issue of whether or not the guarantees provided by Stone's theorem in centralized environments hold in distributed settings.", "In this paper, we propose a general framework for distributed boosting intended for efficient integrating specialized classifiers learned over very large and distributed homogeneous databases that cannot be merged at a single location. Our distributed boosting algorithm can also be used as a parallel classification technique, where a massive database that cannot fit into main computer memory is partitioned into disjoint subsets for a more efficient analysis. In the proposed method, at each boosting round the classifiers are first learned from disjoint datasets and then exchanged amongst the sites. Finally the classifiers are combined into a weighted voting ensemble on each disjoint data set. The ensemble that is applied to an unseen test set represents an ensemble of ensembles built on all distributed sites. In experiments performed on four large data sets the proposed distributed boosting method achieved classification accuracy comparable or even slightly better than the standard boosting algorithm while requiring less memory and less computational time. In addition, the communication overhead of the distributed boosting algorithm is very small making it a viable alternative to the standard boosting for large-scale databases.", "1 Introduction.- 1.1 Distributed Detection Systems.- 1.2 Outline of the Book.- 2 Elements of Detection Theory.- 2.1 Introduction.- 2.2 Bayesian Detection Theory.- 2.3 Minimax Detection.- 2.4 Neyman-Pearson Test.- 2.5 Sequential Detection.- 2.6 Constant False Alarm Rate (CFAR) Detection.- 2.7 Locally Optimum Detection.- 3 Distributed Bayesian Detection: Parallel Fusion Network.- 3.1 Introduction.- 3.2 Distributed Detection Without Fusion.- 3.3 Design of Fusion Rules.- 3.4 Detection with Parallel Fusion Network.- 4 Distributed Bayesian Detection: Other Network Topologies.- 4.1 Introduction.- 4.2 The Serial Network.- 4.3 Tree Networks.- 4.4 Detection Networks with Feedback.- 4.5 Generalized Formulation for Detection Networks.- 5 Distributed Detection with False Alarm Rate Constraints.- 5.1 Introduction.- 5.2 Distributed Neyman-Pearson Detection.- 5.3 Distributed CFAR Detection.- 5.4 Distributed Detection of Weak Signals.- 6 Distributed Sequential Detection.- 6.1 Introduction.- 6.2 Sequential Test Performed at the Sensors.- 6.3 Sequential Test Performed at the Fusion Center.- 7 Information Theory and Distributed Hypothesis Testing.- 7.1 Introduction.- 7.2 Distributed Detection Based on Information Theoretic Criterion.- 7.3 Multiterminal Detection with Data Compression.- Selected Bibliography." ] }

{ "cite_N": [ "@cite_10" ], "mid": [ "2135106139" ], "abstract": [ "Very high dimensional learning systems become theoretically possible when training examples are abundant. The computing cost then becomes the limiting factor. Any efficient learning algorithm should at least take a brief look at each example. But should all examples be given equal attention?This contribution proposes an empirical answer. We first present an online SVM algorithm based on this premise. LASVM yields competitive misclassification rates after a single pass over the training examples, outspeeding state-of-the-art SVM solvers. Then we show how active example selection can yield faster training, higher accuracies, and simpler models, using only a fraction of the training example labels." ] }

{ "cite_N": [ "@cite_13" ], "mid": [ "1988790447" ], "abstract": [ "In the first part of the paper we consider the problem of dynamically apportioning resources among a set of options in a worst-case on-line framework. The model we study can be interpreted as a broad, abstract extension of the well-studied on-line prediction model to a general decision-theoretic setting. We show that the multiplicative weight-update Littlestone?Warmuth rule can be adapted to this model, yielding bounds that are slightly weaker in some cases, but applicable to a considerably more general class of learning problems. We show how the resulting learning algorithm can be applied to a variety of problems, including gambling, multiple-outcome prediction, repeated games, and prediction of points in Rn. In the second part of the paper we apply the multiplicative weight-update technique to derive a new boosting algorithm. This boosting algorithm does not require any prior knowledge about the performance of the weak learning algorithm. We also study generalizations of the new boosting algorithm to the problem of learning functions whose range, rather than being binary, is an arbitrary finite set or a bounded segment of the real line." ] }

{ "cite_N": [ "@cite_15" ], "mid": [ "1834302797" ], "abstract": [ "Wireless sensor networks (WSNs) have attracted considerable attention in recent years and motivate a host of new challenges for distributed signal processing. The problem of distributed or decentralized estimation has often been considered in the context of parametric models. However, the success of parametric methods is limited by the appropriateness of the strong statistical assumptions made by the models. In this paper, a more flexible nonparametric model for distributed regression is considered that is applicable in a variety of WSN applications including field estimation. Here, starting with the standard regularized kernel least-squares estimator, a message-passing algorithm for distributed estimation in WSNs is derived. The algorithm can be viewed as an instantiation of the successive orthogonal projection (SOP) algorithm. Various practical aspects of the algorithm are discussed and several numerical simulations validate the potential of the approach." ] }

{ "cite_N": [ "@cite_6", "@cite_8" ], "mid": [ "2073713788", "2069162168" ], "abstract": [ "What is the best paging algorithm if one has partial information about the possible sequences of page requests? We give a partial answer to this question by presenting the analysis of strongly competitive paging algorithms in the access graph model. This model restricts page requests so that they conform to a notion of locality of reference given by an arbitrary access graph. We first consider optimal algorithms for undirected access graphs. [ Proc. 23rd ACM Symposium on Theory of Computing, 1991, pp. 249--259] define an algorithm, called FAR, and prove that it is within a logarithmic factor of the optimal online algorithm. We prove that FAR is in fact strongly competitive, i.e., within a constant factor of the optimum. For directed access graphs, we present an algorithm that is strongly competitive on structured program graphs---graphs that model a subset of the request sequences of structured programs.", "The Sleator-Tarjan competitive analysis of paging (Comm. ACM28 (1985), 202-208) gives us the ability to make strong theoretical statements about the performance of paging algorithms without making probabilistic assumptions on the input. Nevertheless practitioners voice reservations about the model, citing its inability to discern between LRU and FIFO (algorithms whose performances differ markedly in practice), and the fact that the theoretical comptitiveness of LRU is much larger than observed in practice, In addition, we would like to address the following important question: given some knowledge of a program?s reference pattern, can we use it to improve paging performance on that program? We address these concerns by introducing an important practical element that underlies the philosophy behind paging: locality of reference. We devise a graph-theoretical model, the access graph, for studying locality of reference. We use it to prove results that address the practical concerns mentioned above, In addition, we use our model to address the following questions: How well is LRU likely to perform on a given program? Is there a universal paging algorithm that achieves (nearly) the best possible paging performance on every program? We do so without compromising the benefits of the Sleator-Tarjan model, while bringing it closer to practice." ] }

{ "cite_N": [ "@cite_11" ], "mid": [ "2068714069" ], "abstract": [ "In this paper we devise new paging heuristics motivated by the access graph model of paging. Unlike the access graph model and the related Markov paging model our heuristics are truly on-line in that we do not assume any prior knowledge of the program just about to be executed. The Least Recently Used heuristic for paging is remarkably good, and is known experimentally to be superior to many of the suggested alternatives on real program traces. Experiments we ve performed suggest that our heuristics beat LRU fairly consistently, over a wide range of cache sizes and programs. The number of page faults can be as low as 1 2 the number of page faults for LRU and is on average 7 to 9 percent less than the number of faults for LRU. (Depending on how this average is computed.) We have built a program tracer that gives the page access sequence for real program executions of 200 - 3,300 thousand page access requests, and our simulations are based on 25 of these program traces. Overall, we have performed several thousand such simulations. While we have no real evidence to suggest that the programs we ve traced are typical in any sense, we havemore » made use of an experimental open_quotes protocol close_quotes designed to avoid experimenter bias. We strongly emphasize that our results are only preliminary and that much further work needs to be done.« less" ] }

{ "cite_N": [ "@cite_37", "@cite_55", "@cite_3", "@cite_56", "@cite_15", "@cite_13", "@cite_66" ], "mid": [ "2071764857", "", "", "2165923712", "2051051926", "1997124098", "1970006170" ], "abstract": [ "We prove that the 1984 protocol of Bennett and Brassard (BB84) for quantum key distribution is secure. We first give a key distribution protocol based on entanglement purification, which can be proven secure using methods from Lo and Chau's proof of security for a similar protocol. We then show that the security of this protocol implies the security of BB84. The entanglement purification based protocol uses Calderbank-Shor-Steane codes, and properties of these codes are used to remove the use of quantum computation from the Lo-Chau protocol.", "", "", "Shor and Preskill (see Phys. Rev. Lett., vol.85, p.441, 2000) have provided a simple proof of security of the standard quantum key distribution scheme by Bennett and Brassard (1984) by demonstrating a connection between key distribution and entanglement purification protocols (EPPs) with one-way communications. Here, we provide proofs of security of standard quantum key distribution schemes, Bennett and Brassard and the six-state scheme, against the most general attack, by using the techniques of two-way entanglement purification. We demonstrate clearly the advantage of classical post-processing with two-way classical communications over classical post-processing with only one-way classical communications in quantum key distribution (QKD). This is done by the explicit construction of a new protocol for (the error correction detection and privacy amplification of) Bennett and Brassard that can tolerate a bit error rate of up to 18.9 , which is higher than what any Bennett and Brassard scheme with only one-way classical communications can possibly tolerate. Moreover, we demonstrate the advantage of the six-state scheme over Bennett and Brassard by showing that the six-state scheme can strictly tolerate a higher bit error rate than Bennett and Brassard. In particular, our six-state protocol can tolerate a bit error rate of 26.4 , which is higher than the upper bound of 25 bit error rate for any secure Bennett and Brassard protocol. Consequently, our protocols may allow higher key generation rate and remain secure over longer distances than previous protocols. Our investigation suggests that two-way entanglement purification is a useful tool in the study of advantage distillation, error correction, and privacy amplification protocols.", "Practical application of the generalized Bells theorem in the so-called key distribution process in cryptography is reported. The proposed scheme is based on the Bohms version of the Einstein-Podolsky-Rosen gedanken experiment and Bells theorem is used to test for eavesdropping. © 1991 The American Physical Society.", "Ekert has described a cryptographic scheme in which Einstein-Podolsky-Rosen (EPR) pairs of particles are used to generate identical random numbers in remote places, while Bell's theorem certifies that the particles have not been measured in transit by an eavesdropper. We describe a related but simpler EPR scheme and, without invoking Bell's theorem, prove it secure against more general attacks, including substitution of a fake EPR source. Finally we show our scheme is equivalent to the original 1984 key distribution scheme of Bennett and Brassard, which uses single particles instead of EPR pairs.", "Quantum key distribution is widely thought to offer unconditional security in communication between two users. Unfortunately, a widely accepted proof of its security in the presence of source, device, and channel noises has been missing. This long-standing problem is solved here by showing that, given fault-tolerant quantum computers, quantum key distribution over an arbitrarily long distance of a realistic noisy channel can be made unconditionally secure. The proof is reduced from a noisy quantum scheme to a noiseless quantum scheme and then from a noiseless quantum scheme to a noiseless classical scheme, which can then be tackled by classical probability theory." ] }

{ "cite_N": [ "@cite_30", "@cite_67", "@cite_54", "@cite_52", "@cite_44" ], "mid": [ "2119098193", "2079729767", "", "2114805880", "1980534149" ], "abstract": [ "We address the question whether quantum memory is more powerful than classical memory. In particular, we consider a setting where information about a random n-bit string X is stored in s classical or quantum bits, for s<n, i.e., the stored information is bound to be only partial. Later, a randomly chosen predicate F about X has to be guessed using only the stored information. The maximum probability of correctly guessing F(X) is then compared for the cases where the storage device is classical or quantum mechanical, respectively. We show that, despite the fact that the measurement of quantum bits can depend arbitrarily on the predicate F, the quantum advantage is negligible already for small values of the difference n-s. Our setting generalizes the setting of who considered the problem of guessing an arbitrary bit (i.e., one of the n bits) of X. An implication for cryptography is that privacy amplification by universal hashing remains essentially equally secure when the adversary's memory is allowed to be quantum rather than only classical. Since privacy amplification is a main ingredient of many quantum key distribution (QKD) protocols, our result can be used to prove the security of QKD in a generic way.", "We investigate a general class of quantum key distribution (QKD) protocols using one-way classical communication. We show that full security can be proven by considering only collective attacks. We derive computable lower and upper bounds on the secret-key rate of those QKD protocols involving only entropies of two-qubit density operators. As an illustration of our results, we determine new bounds for the Bennett-Brassard 1984, the 6-state, and the Bennett 1992 protocols. We show that in all these cases the first classical processing that the legitimate partners should apply consists in adding noise.", "", "Privacy amplification is the art of shrinking a partially secret string Z to a highly secret key S. We show that, even if an adversary holds quantum information about the initial string Z, the key S obtained by two-universal hashing is secure, according to a universally composable security definition. Additionally, we give an asymptotically optimal lower bound on the length of the extractable key S in terms of the adversary's (quantum) knowledge about Z. Our result has applications in quantum cryptography. In particular, it implies that many of the known quantum key distribution protocols are universally composable.", "We present a technique for proving the security of quantum-key-distribution (QKD) protocols. It is based on direct information-theoretic arguments and thus also applies if no equivalent entanglement purification scheme can be found. Using this technique, we investigate a general class of QKD protocols with one-way classical post-processing. We show that, in order to analyze the full security of these protocols, it suffices to consider collective attacks. Indeed, we give new lower and upper bounds on the secret-key rate which only involve entropies of two-qubit density operators and which are thus easy to compute. As an illustration of our results, we analyze the Bennett-Brassard 1984, the six-state, and the Bennett 1992 protocols with one-way error correction and privacy amplification. Surprisingly, the performance of these protocols is increased if one of the parties adds noise to the measurement data before the error correction. In particular, this additional noise makes the protocols more robust against noise in the quantum channel." ] }

{ "cite_N": [ "@cite_41", "@cite_38", "@cite_4" ], "mid": [ "", "2062768305", "2953325427" ], "abstract": [ "", "We present here an information theoretic study of Gaussian collective attacks on the continuous variable key distribution protocols based on Gaussian modulation of coherent states. These attacks, overlooked in previous security studies, give a finite advantage to the eavesdropper in the experimentally relevant lossy channel, but are not powerful enough to reduce the range of the reverse reconciliation protocols. Secret key rates are given for the ideal case where Bob performs optimal collective measurements, as well as for the realistic cases where he performs homodyne or heterodyne measurements. We also apply the generic security proof of Christiandl et. al. [quant-ph 0402131] to obtain unconditionally secure rates for these protocols.", "We study quantum key distribution with standard weak coherent states and show, rather counter-intuitively, that the detection events originated from vacua can contribute to secure key generation rate, over and above the best prior art result. Our proof is based on a communication complexity quantum memory argument." ] }

{ "cite_N": [ "@cite_13" ], "mid": [ "2101963262" ], "abstract": [ "We present Greedy Perimeter Stateless Routing (GPSR), a novel routing protocol for wireless datagram networks that uses the positions of routers and a packet's destination to make packet forwarding decisions. GPSR makes greedy forwarding decisions using only information about a router's immediate neighbors in the network topology. When a packet reaches a region where greedy forwarding is impossible, the algorithm recovers by routing around the perimeter of the region. By keeping state only about the local topology, GPSR scales better in per-router state than shortest-path and ad-hoc routing protocols as the number of network destinations increases. Under mobility's frequent topology changes, GPSR can use local topology information to find correct new routes quickly. We describe the GPSR protocol, and use extensive simulation of mobile wireless networks to compare its performance with that of Dynamic Source Routing. Our simulations demonstrate GPSR's scalability on densely deployed wireless networks." ] }

{ "cite_N": [ "@cite_4", "@cite_8", "@cite_3", "@cite_6", "@cite_2", "@cite_5" ], "mid": [ "180909918", "2167477163", "2039252979", "1991523989", "2022390945", "1659568777" ], "abstract": [ "", "Sensor networks not only have the potential to change the way we use, interact with, and view computers, but also the way we use, interact with, and view the world around us. In order to maximize the effectiveness of sensor networks, one has to identify, examine, understand, and provide solutions for the fundamental problems related to wireless embedded sensor networks. We believe that one of such problems is to determine how well the sensor network monitors the instrumented area. These problems are usually classified as coverage problems. There already exist several methods that have been proposed to evaluate a sensor network's coverage.We start from one of such method and provide a new approach to complement it. The method of using the minimal exposure path to quantify coverage has been optimally solved using a numerical approximation approach. The minimal exposure path can be thought of as the worst-case coverage of a sensor network. Our first goal is to develop an efficient localized algorithm that enables a sensor network to determine its minimal exposure path. The theoretical highlight of this paper is the closed-form solution for minimal exposure in the presence of a single sensor. This solution is the basis for the new and significantly faster localized approximation algorithm that reduces the theoretical complexity of the previous algorithm. On the other hand, we introduce a new coverage problem - the maximal exposure path - which is in a sense the best-case coverage path for a sensor network. We prove that the maximal exposure path problem is NP-hard, and thus, we provide heuristics to generate approximate solutions.In addition, we demonstrate the effectiveness of our algorithms through several simulations. In the case of the minimal single-source minimal exposure path, we use variational calculus to determine exact solutions. For the case of maximal exposure, we use networks with varying numbers of sensors and exposure models.", "We develop distributed algorithms for self-organizing sensor networks that respond to directing a target through a region. The sensor network models the danger levels sensed across its area and has the ability to adapt to changes. It represents the dangerous areas as obstacles. A protocol that combines the artificial potential field of the sensors with the goal location for the moving object guides the object incrementally across the network to the goal, while maintaining the safest distance to the danger areas. We give the analysis to the protocol and report on hardware experiments using a physical sensor network consisting of Mote sensors.", "Wireless ad-hoc sensor networks will provide one of the missing connections between the Internet and the physical world. One of the fundamental problems in sensor networks is the calculation of coverage. Exposure is directly related to coverage in that it is a measure of how well an object, moving on an arbitrary path, can be observed by the sensor network over a period of time. In addition to the informal definition, we formally define exposure and study its properties. We have developed an efficient and effective algorithm for exposure calculation in sensor networks, specifically for finding minimal exposure paths. The minimal exposure path provides valuable information about the worst case exposure-based coverage in sensor networks. The algorithm works for any given distribution of sensors, sensor and intensity models, and characteristics of the network. It provides an unbounded level of accuracy as a function of run time and storage. We provide an extensive collection of experimental results and study the scaling behavior of exposure and the proposed algorithm for its calculation.", "In this paper we investigate efficient strategies for supporting on-demand information dissemination and gathering in large-scale vwireless sensor networks. In particular, we propose a \"comb-needle\" discovery support model resembling an ancient method: use a comb to help find a needle in sands or a haystack. The model combines push and pull for information dissemination and gathering. The push component features data duplication in a linear neighborhood of each node. The pull component features a dynamic formation of an on-demand routing structure resembling a comb. The comb-needle model enables us to investigate the cost of a spectrum of push and pull combinations for supporting discovery and query in large scale sensor networks. Our result shows that the optimal routing structure depends on the frequency of query occurrence and the spatial-temporal frequency of related events in the network. The benefit of balancing push and pull for discovery in large scale geometric networks are demonstrated. We also raise the issue of query coverage in unreliable networks and investigate how redundancy can improve the coverage via both theoretical analysis and simulation. Last, we study adaptive strategies for the case where the frequencies of query and events are unknown a priori and time-varying.", "" ] }

{ "cite_N": [ "@cite_36", "@cite_26", "@cite_7" ], "mid": [ "2088429233", "179202249", "2072475455" ], "abstract": [ "LOCKSS (Lots Of Copies Keep Stuff Safe) is a tool designed for libraries to use to ensure their community's continued access to web-published scientific journals. LOCKSS allows libraries to take custody of the material to which they subscribe, in the same way they do for paper, and to preserve it. By preserving it they ensure that, for their community, links and searches continue to resolve to the published material even if it is no longer available from the publisher. Think of it as the digital equivalent of stacks where an authoritative copy of material is always available rather than the digital equivalent of an archive. LOCKSS allows libraries to run web caches for specific journals. These caches collect content as it is published and are never flushed. They cooperate in a peer-to-peer network to detect and repair damaged or missing pages. The caches run on generic PC hardware using open-source software and require almost no skilled administration, making the cost of preserving a journal manageable.", "", "Recently the Library of Congress began developing a strategy for the preservation of digital content. Efforts have focused on the need to select, harvest, describe, access and preserve Web resources. This poster focuses on the Library's initial investigation and evaluation of Web harvesting software tools." ] }

{ "cite_N": [ "@cite_27", "@cite_34", "@cite_21", "@cite_16" ], "mid": [ "2117044215", "2024882820", "2005783315", "2091712605" ], "abstract": [ "This paper presents a transaction-time HTTP server, called TTApache that supports document versioning. A document often consists of a main file formatted in HTML or XML and several included files such as images and stylesheets. A change to any of the files associated with a document creates a new version of that document. To construct a document version history, snapshots of the document's files are obtained over time. Transaction times are associated with each file version to record the version's lifetime. The transaction time is the system time of the edit that created the version. Accounting for transaction time is essential to supporting audit queries that delve into past document versions and differential queries that pinpoint differences between two versions. TTApache performs automatic versioning when a document is read thereby removing the burden of versioning from document authors. Since some versions may be created but never read, TTApache distinguishes between known and assumed versions of a document. TTApache has a simple query language to retrieve desired versions. A browser can request a specific version, or the entire history of a document. Queries can also rewrite links and references to point to current or past versions. Over time, the version history of a document continually grows. To free space, some versions can be vacuumed. Vacuuming a version however changes the semantics of requests for that version. This paper presents several policies for vacuuming versions and strategies for accounting for vacuumed versions in queries.", "It is important to provide long-term preservation of digital data even when those data are stored in an unreliable system such as a filesystem, a legacy database, or even the World Wide Web. In this paper we focus on the problem of archiving the contents of a Web site without disrupting users who maintain the site. We propose an archival storage system, the InfoMonitor, in which a reliable archive is integrated with an unmodified existing store. Implementing such a system presents various challenges related to the mismatch of features between the components such as differences in naming and data manipulation operations. We examine each of these issues as well as solutions for the conflicts that arise. We also discuss our experience using the InfoMonitor to archive the Stanford Database Group's Web site.", "The growth of the World Wide Web holds great promise for universal online information access. New information is constantly being made available for users. However, the information accessible on the Web changes constantly. These changes may occur as modifications to both the content and the location of previously existing Web resources. As these changes occur, the accessibility to past versions of such Web resources is often lost. This paper presents an approach to provide content persistence of Web resources by organizing collections of historical Web resources in a distributed configuration management system to allow online, read-only access to the versioned resources.", "The Web contains so much information that it is almost beyond measure. How do users manage the useful information that they have seen while screening out the rest that doesn't interest them? Bookmarks help, but bookmarking a page doesn't guarantee that it will be available forever. Search engines are becoming more powerful, but they can't be customized based on the access history of individual users. This paper suggests that a better alternative to managing web information is through a middleware approach based on iPROXY, a programmable proxy server. iPROXY offers a suite of archiving, retrieval, and searching services. It can extend a URL to include commands that archive and retrieve pages. Its modular architecture allows users to plug in new features without having to change existing browsers or servers. Once installed on a network, iPROXY can be accessed by users using different browsers and devices. Internet service providers who offer customers iPROXY will be free to develop new services without having to wait for the dominant browsers to be updated." ] }

{ "cite_N": [ "@cite_19" ], "mid": [ "2080676333" ], "abstract": [ "In this short paper we estimate the size of the public indexable web at 11.5 billion pages. We also estimate the overlap and the index size of Google, MSN, Ask Teoma and Yahoo!" ] }

{ "cite_N": [ "@cite_18", "@cite_14", "@cite_4", "@cite_7", "@cite_28", "@cite_21", "@cite_1", "@cite_32", "@cite_17", "@cite_5", "@cite_12", "@cite_11" ], "mid": [ "1987582408", "2142917009", "2022940918", "95741843", "", "1600548747", "2120228516", "2109745615", "2002425684", "10991463", "1484844389", "2082841997" ], "abstract": [ "This paper establishes a link between two principal tools for the analysis of network traffic, namely, effective bandwidth and network calculus. It is shown that a general version of effective bandwidth can be expressed within the framework of a probabilistic version of the network calculus, where both arrivals and service are specified in terms of probabilistic bounds. By formulating well-known effective bandwidth expressions in terms of probabilistic envelope functions, the developed network calculus can be applied to a wide range of traffic types, including traffic that has self-similar characteristics. As applications, probabilistic lower bounds are presented on the service given by three different scheduling algorithms: static priority, earliest deadline first, and generalized processor sharing. Numerical examples show the impact of specific traffic models and scheduling algorithms on the multiplexing gain in a network.", "We introduce the concept of generalized stochastically bounded burstiness (gSBB) for Internet traffic, the tail distribution of whose burstiness can be bounded by a decreasing function in a function class with few restrictions. This new concept extends the concept of stochastically bounded burstiness (SBB) introduced by previous researchers to a much larger extent - while the SBB model can apply to Gaussian self-similar input processes, such as fractional Brownian motion, gSBB traffic contains non-Gaussian self-similar input processes, such as spl alpha -stable self-similar processes, which are not SBB in general. We develop a network calculus for gSBB traffic. We characterize gSBB traffic by the distribution of its queue size. We explore the property of sums of gSBB traffic and the relation of input and output processes. We apply this calculus to a work-conserving system shared by a number of gSBB sources, to analyze the behavior of output traffic for each source and to estimate the probabilistic bounds for delays. We expect this new calculus to be of particular interest in the implementation of services with statistical qualitative guarantees.", "A network calculus is developed for processes whose burstiness is stochastically bounded by general decreasing functions. This calculus is useful for a large class of input processes, including important processes exhibiting \"subexponentially bounded burstiness\" such as fractional Brownian motion. Moreover, it allows judicious capture of the salient features of real-time traffic, such as the \"cell\" and \"burst\" characteristics of multiplexed traffic. This accurate characterization is achieved by setting the bounding function as a sum of exponentials.", "", "", "Many communication networks such as wireless networks only provide stochastic service guarantees. For analyzing stochastic service guarantees, research efforts have been made in the past few years to develop stochastic network calculus, a probabilistic version of (min, +) deterministic network calculus. However, many challenges have made the development difficult. Some of them are closely related to server modeling, which include output characterization, concatenation property, stochastic backlog guarantee, stochastic delay guarantee, and per-flow service under aggregation. In this paper, we propose a server model, called stochastic service curve to facilitate stochastic service guarantee analysis. We show that with the concept of stochastic service curve, these challenges can be well addressed. In addition, we introduce strict stochastic server to help find the stochastic service curve of a stochastic server, which characterizes the service of the server by two stochastic processes: an ideal service process and an impairment process.", "The deterministic network calculus offers an elegant framework for determining delays and backlog in a network with deterministic service guarantees to individual traffic flows. A drawback of the deterministic network calculus is that it only provides worst-case bounds. Here we present a network calculus for statistical service guarantees, which can exploit the statistical multiplexing gain of sources. We introduce the notion of an effective service curve as a probabilistic bound on the service received by an individual flow, and construct an effective service curve for a network where capacities are provisioned exclusively to aggregates of flows. Numerical examples demonstrate that the calculus is able to extract a significant amount of multiplexing gain in networks with a large number of flows.", "A method for evaluating the performance of packet switching communication networks under a fixed, session-based, routing strategy is proposed. The approach is based on properly bounding the probability distribution functions of the system input processes. The suggested bounds which are decaying exponentials, possess three convenient properties. When the inputs to an isolated network element are all bounded, they result in bounded outputs and assure that the delays and queues in this element have exponentially decaying distributions. In some network settings, bounded inputs result in bounded outputs. Natural traffic processes can be shown to satisfy such bounds. Consequently, this method enables the analysis of various previously intractable setups. Sufficient conditions are provided for the stability of such networks, and derive upper bounds for the parameters of network performance are derived. >", "In most network models for quality of service support, the communication links interconnecting the switches and gateways are assumed to have fixed bandwidth and zero error rate. This assumption of steadiness, especially in a heterogeneous internet-working environment, might be invalid owing to subnetwork multiple-access mechanism, link-level flow error control, and user mobility. Techniques are presented in this paper to characterize and analyze work-conserving communication nodes with varying output rate. In the deterministic approach, the notion of \"fluctuation constraint,\" analogous to the \"burstiness constraint\" for traffic characterization, is introduced to characterize the node. In the statistical approach, the variable-rate output is modelled as an \"exponentially bounded fluctuation\" process in a way similar to the \"exponentially bounded burstiness\" method for traffic modelling. Based on these concepts, deterministic and statistical bounds on queue size and packet delay in isolated variable-rate communication server-nodes are derived, including cases of single-input and multiple-input under first-come-first-serve queueing. Queue size bounds are shown to be useful for buffer requirement and packet loss probability estimation at individual nodes. Our formulations also facilitate the computation of end-to-end performance bounds across a feedforward network of variable-rate server-nodes. Several numerical examples of interest are given in the discussion.", "The issue of Quality of Service (QoS) performance analysis in packet switching networks has drawn a lot of attention in the networking community in recent years. There is a lot of work including an elegant theory under the name of network calculus focusing on analysis of deterministic worst case QoS performance bounds. In the meantime, other researchers have studied the stochastic QoS performance for specific schedulers. As yet, there has been no systematic investigation and analysis of end-to-end stochastic QoS performance. On the other hand, most of the previous work on deterministic QoS analysis or stochastic QoS analysis only considered a server which provides deterministic service, i.e. deterministically bounded rate service. Few works have considered the behavior of a stochastic server providing input flows with variable rate service. In this report, we propose a stochastic network calculus to systematically analyze the end-to-end stochastic QoS performance of a system with stochastically bounded input traffic over a series of deterministic and stochastic servers. The proposed framework is also applied to analyze per-flow stochastic QoS performance since a server serving an aggregate of flows can be regarded as a stochastic server for individual flows within the aggregate under aggregate scheduling. Keywords Stochastic Modeling, Network Calculus, Quality of Service", "We propose a probabilistic characterization of network traffic. This characterization can handle traffic with heavy-tailed distributions in performance analysis. We show that queue size, output traffic, virtual delay, aggregate traffic, etc. at various points in a network can easily be characterized within the framework. This characterization is measurable and allows for a simple probabilistic method for regulating network traffic. All of these properties of the proposed characterization enable a systematic approach for providing end-to-end probabilistic QoS guarantees", "The stochastic network calculus is an evolving new methodology for backlog and delay analysis of networks that can account for statistical multiplexing gain. This paper advances the stochastic network calculus by deriving a network service curve, which expresses the service given to a flow by the network as a whole in terms of a probabilistic bound. The presented network service curve permits the calculation of statistical end-to-end delay and backlog bounds for broad classes of arrival and service distributions. The benefits of the derived service curve are illustrated for the exponentially bounded burstiness (EBB) traffic model. It is shown that end-to-end performance measures computed with a network service curve are bounded by O(Hlog H), where H is the number of nodes traversed by a flow. Using currently available techniques that compute end-to-end bounds by adding single node results, the corresponding performance measures are bounded by O(H3)." ] }

{ "cite_N": [ "@cite_38", "@cite_34" ], "mid": [ "2062706778", "1985431233" ], "abstract": [ "Networks that support multiple services through \"link-sharing\" must address the fundamental conflicting requirement between isolation among service classes to satisfy each class' quality of service requirements, and statistical sharing of resources for efficient network utilization. While a number of service disciplines have been devised which provide mechanisms to both isolate flows and fairly share excess capacity, admission control algorithms are needed which exploit the effects of inter-class resource sharing. In this paper, we develop a framework of using statistical service envelopes to study inter-class statistical resource sharing. We show how this service envelope enables a class to over-book resources beyond its deterministically guaranteed capacity by statistically characterizing the excess service available due to fluctuating demands of other service classes. We apply our techniques to several multi-class schedulers, including generalized processor sharing, and design new admission control algorithms for multi-class link-sharing environments. We quantify the utilization gains of our approach with a set of experiments using long traces of compressed video.", "We present a technique for computing upper bounds on the distribution of individual per-session performance measures such as delay and buffer occupancy for networks in which sessions may be routed over several “hops.” Our approach is based on first stochastically bounding the distribution of the number of packets (or cells) which can be generated by each traffic source over various lengths of time and then “pushing” these bounds (which are then shown to hold over new time interval lengths at various network queues) through the network on a per-session basis. Session performance bounds can then be computed once the stochastic bounds on the arrival process have been characterized for each session at all network nodes. A numerical example is presented and the resulting distributional bounds compared with simulation as well as with a point-valued worst-case performance bound." ] }

{ "cite_N": [ "@cite_8", "@cite_24", "@cite_15", "@cite_10", "@cite_20" ], "mid": [ "2090888999", "2112919802", "2115632051", "2111764355", "1978905175" ], "abstract": [ "A crucial problem for the efficient design and management of integrated services networks is how to best allocate network resources for heterogeneous and bursty traffic streams in multiplexers that support prioritized service disciplines. In this paper, we introduce a new approach for determining per-connection performance parameters such as delay-bound violation probability and loss probability in multi-service networks. The approach utilizes a traffic characterization consisting of the variances of a stream's rate distribution over multiple interval lengths, which captures its burstiness properties and autocorrelation structure. From this traffic characterization, we provide a simple and efficient resource allocation algorithm by deriving stochastic delay-bounds for static priority schedulers and employing a Gaussian approximation over intervals. To evaluate the scheme, we perform trace-driven simulation experiments with long traces of MPEG-compressed video and show that our approach is accurate enough to capture most of the inherent statistical multiplexing gain, achieving average network utilizations of up to 90 for these traces and substantially outperforming previous \"effective bandwidth\" techniques.", "Considers stochastic linear systems under the max-plus algebra. For such a system, the states are governed by the recursive equation X sub n =A sub n spl otimes X sub n-1 spl oplus U sub n with the initial condition condition X sub 0 =x sub 0 . By transforming the linear system under the max-plus algebra into a sublinear system under the usual algebra, we establish various exponential upper bounds for the tail distributions of the states X sub n under the independently identically distributed (i.i.d.) assumption on (A sub n ,U sub n ) sub 1 n spl ges 1 and a couple of regularity conditions on (A sub 1 ,U sub 1 ) and the initial condition x sub 0 . These upper bounds are related to the spectral radius (or the Perron-Frobenius eigenvalue) of the nonnegative matrix in which each element is the moment generating function of the corresponding element in the state-feedback matrix A sub 1 . In particular, we have Kingman's upper bound for GI GI 1 queue when the system is one-dimensional. We also show that some of these upper bounds can be achieved if A sub 1 is lower triangular. These bounds are applied to some commonly used systems to derive new results or strengthen known results.", "To facilitate the efficient support of quality of service (QoS) in next-generation wireless networks, it is essential to model a wireless channel in terms of connection-level QoS metrics such as data rate, delay, and delay-violation probability. However, the existing wireless channel models, i.e., physical-layer channel models, do not explicitly characterize a wireless channel in terms of these QoS metrics. In this paper, we propose and develop a link-layer channel model termed effective capacity (EC). In this approach, we first model a wireless link by two EC functions, namely, the probability of nonempty buffer, and the QoS exponent of a connection. Then, we propose a simple and efficient algorithm to estimate these EC functions. The physical-layer analogs of these two link-layer EC functions are the marginal distribution (e.g., Rayleigh-Ricean distribution) and the Doppler spectrum, respectively. The key advantages of the EC link-layer modeling and estimation are: 1) ease of translation into QoS guarantees, such as delay bounds; 2) simplicity of implementation; and 3) accuracy, and hence, efficiency in admission control and resource reservation. We illustrate the advantage of our approach with a set of simulation experiments, which show that the actual QoS metric is closely approximated by the QoS metric predicted by the EC link-layer model, under a wide range of conditions.", "We present two types of stability problems: 1) conditions for queueing networks that render bounded queue lengths and bounded delay for customers, and 2) conditions for queueing networks in which the queue length distribution of a queue has an exponential tail with rate spl theta . To answer these two types of stability problems, we introduce two new notions of traffic characterization: minimum envelope rate (MER) and MER with respect to spl theta . We also develop a set of rules for network operations such as superposition, input-output relation of a single queue, and routing. Specifically, we show that: 1) the MER of a superposition process is less than or equal to the sum of the MER of each process, 2) a queue is stable in the sense of bounded queue length if the MER of the input traffic is smaller than the capacity, 3) the MER of a departure process from a stable queue is less than or equal to that of the input process, and 4) the MER of a routed process from a departure process is less than or equal to the MER of the departure process multiplied by the MER of the routing process. Similar results hold for MER with respect to spl theta under a further assumption of independence. For single class networks with nonfeedforward routing, we provide a new method to show that similar stability results hold for such networks under the first come, first served policy. Moreover, when restricting to the family of two-state Markov modulated arrival processes, the notion of MER with respect to spl theta is shown to be equivalent to the recently developed notion of effective bandwidth in communication networks. >", "From the Publisher: Providing performance guarantees is one of the most important issues for future telecommunication networks. This book describes theoretical developments in performance guarantees for telecommunication networks from the last decade. Written for the benefit of graduate students and scientists interested in telecommunications-network performance this book consists of two parts." ] }

{ "cite_N": [ "@cite_29", "@cite_14", "@cite_32" ], "mid": [ "2411715191", "32779056", "1674877186" ], "abstract": [ "", "The timely and accurate detection of computer and network system intrusions has always been an elusive goal for system administrators and information security researchers. Existing intrusion detection approaches require either manual coding of new attacks in expert systems or the complete retraining of a neural network to improve analysis or learn new attacks. This paper presents a new approach to applying adaptive neural networks to intrusion detection that is capable of autonomously learning new attacks rapidly through the use of a modified reinforcement learning method that uses feedback from the protected system. The approach has been demonstrated to be extremely effective in learning new attacks, detecting previously learned attacks in a network data stream, and in autonomously improving its analysis over time using feedback from the protected system.", "Network intrusion detection systems (NIDS) are an important part of any network security architecture. They provide a layer of defense which monitors network traffic for predefined suspicious activity or patterns, and alert system administrators when potential hostile traffic is detected. Commercial NIDS have many differences, but Information Systems departments must face the commonalities that they share such as significant system footprint, complex deployment and high monetary cost. Snort was designed to address these issues." ] }

{ "cite_N": [ "@cite_19", "@cite_18", "@cite_6" ], "mid": [ "1982304603", "", "2045064676" ], "abstract": [ "With the continuous evolution of the types of attacks against computer networks, traditional intrusion detection systems, based on pattern matching and static signatures, are increasingly limited by their need of an up-to-date and comprehensive knowledge base. Data mining techniques have been successfully applied in host-based intrusion detection. Applying data mining techniques on raw network data, however, is made difficult by the sheer size of the input; this is usually avoided by discarding the network packet contents.In this paper, we introduce a two-tier architecture to overcome this problem: the first tier is an unsupervised clustering algorithm which reduces the network packets payload to a tractable size. The second tier is a traditional anomaly detection algorithm, whose efficiency is improved by the availability of data on the packet payload content.", "", "Outlier detection is a fundamental issue in data mining, specifically in fraud detection, network intrusion detection, network monitoring, etc. SmartSifter is an outlier detection engine addressing this problem from the viewpoint of statistical learning theory. This paper provides a theoretical basis for SmartSifter and empirically demonstrates its effectiveness. SmartSifter detects outliers in an on-line process through the on-line unsupervised learning of a probabilistic model (using a finite mixture model) of the information source. Each time a datum is input SmartSifter employs an on-line discounting learning algorithm to learn the probabilistic model. A score is given to the datum based on the learned model with a high score indicating a high possibility of being a statistical outlier. The novel features of SmartSifter are: (1) it is adaptive to non-stationary sources of datas (2) a score has a clear statistical information-theoretic meanings (3) it is computationally inexpensives and (4) it can handle both categorical and continuous variables. An experimental application to network intrusion detection shows that SmartSifter was able to identify data with high scores that corresponded to attacks, with low computational costs. Further experimental application has identified a number of meaningful rare cases in actual health insurance pathology data from Australia's Health Insurance Commission." ] }

{ "cite_N": [ "@cite_28", "@cite_18", "@cite_26" ], "mid": [ "2162076967", "2082199994", "2097625638" ], "abstract": [ "We formulate the delay-tolerant networking routing problem, where messages are to be moved end-to-end across a connectivity graph that is time-varying but whose dynamics may be known in advance. The problem has the added constraints of finite buffers at each node and the general property that no contemporaneous end-to-end path may ever exist. This situation limits the applicability of traditional routing approaches that tend to treat outages as failures and seek to find an existing end-to-end path. We propose a framework for evaluating routing algorithms in such environments. We then develop several algorithms and use simulations to compare their performance with respect to the amount of knowledge they require about network topology. We find that, as expected, the algorithms using the least knowledge tend to perform poorly. We also find that with limited additional knowledge, far less than complete global knowledge, efficient algorithms can be constructed for routing in such environments. To the best of our knowledge this is the first such investigation of routing issues in DTNs.", "The developments in the space technologies are enabling the realization of deep space scientific missions such as Mars exploration. InterPlaNetary (IPN) Internet is expected to be the next step in the design and development of deep space networks as the Internet of the deep space planetary networks. However, there exist significant challenges to be addressed for the realization of this objective. Many researchers and several international organizations are currently engaged in defining and addressing these challenges and developing the required technologies for the realization of the InterPlaNetary Internet. In this paper, the current status of the research efforts to realize the InterPlaNetary Internet objective is captured. The communication architecture is presented, and the challenges posed by the several aspects of the InterPlaNetary Internet are introduced. The existing algorithms and protocols developed for each layer and the other related work are explored, and their shortcomings are pointed out along with the open research issues for the realization of the InterPlaNetary Internet. The objective of this survey is to motivate the researchers around the world to tackle these challenging problems and help to realize the InterPlaNetary Internet.", "Increasingly, network applications must communicate with counterparts across disparate networking environments characterized by significantly different sets of physical and operational constraints; wide variations in transmission latency are particularly troublesome. The proposed Interplanetary Internet, which must encompass both terrestrial and interplanetary links, is an extreme case. An architecture based on a \"least common denominator\" protocol that can operate successfully and (where required) reliably in multiple disparate environments would simplify the development and deployment of such applications. The Internet protocols are ill suited for this purpose. We identify three fundamental principles that would underlie a delay-tolerant networking (DTN) architecture and describe the main structural elements of that architecture, centered on a new end-to-end overlay network protocol called Bundling. We also examine Internet infrastructure adaptations that might yield comparable performance but conclude that the simplicity of the DTN architecture promises easier deployment and extension." ] }

{ "cite_N": [ "@cite_7", "@cite_9", "@cite_3", "@cite_2", "@cite_5" ], "mid": [ "", "2104776149", "2165995633", "2107059366", "1626653188" ], "abstract": [ "", "An empirical study of the accuracy of five different curvature estimation techniques, using synthetic range images and images obtained from three range sensors, is presented. The results obtained highlight the problems inherent in accurate estimation of curvatures, which are second-order quantities, and thus highly sensitive to noise contamination. The numerical curvature estimation methods are found to perform about as accurately as the analytic techniques, although ensemble estimates of overall surface curvature such as averages are unreliable unless trimmed estimates are used. The median proved to be the best estimator of location. As an exception, it is shown theoretically that zero curvature can be fairly reliably detected, with appropriate selection of threshold values. >", "This paper takes a systematic look at calculating the curvature of surfaces represented by triangular meshes. We have developed a suite of test cases for assessing the sensitivity of curvature calculations, to noise, mesh resolution, and mesh regularity. These tests are applied to existing discrete curvature approximation techniques and three common surface fitting methods (polynomials, radial basis functions and conics). We also introduce a modification to the standard parameterization technique. Finally, we examine the behaviour of the curvature calculation techniques in the context of segmentation.", "Approximations to the surface normal and to the Gaussian curvature of a smooth surface are often required when the surface is defined by a set of discrete points. The accuracy of an approximation can be measured using asymptotic analysis. The errors of several approximations to the surface normal and to the Gaussian curvature are compared. © 2000 Elsevier Science B.V. All rights reserved.", "This paper proposes a unified and consistent set of flexible tools to approximate important geometric attributes, including normal vectors and curvatures on arbitrary triangle meshes. We present a consistent derivation of these first and second order differential properties using averaging Voronoi cells and the mixed Finite-Element Finite-Volume method, and compare them to existing formulations. Building upon previous work in discrete geometry, these operators are closely related to the continuous case, guaranteeing an appropriate extension from the continuous to the discrete setting: they respect most intrinsic properties of the continuous differential operators. We show that these estimates are optimal in accuracy under mild smoothness conditions, and demonstrate their numerical quality. We also present applications of these operators, such as mesh smoothing, enhancement, and quality checking, and show results of denoising in higher dimensions, such as for tensor images." ] }

{ "cite_N": [ "@cite_30", "@cite_35", "@cite_27", "@cite_17" ], "mid": [ "2116173498", "2100776472", "2130476447", "2149055390" ], "abstract": [ "We study networks that connect points in geographic space, such as transportation networks and the Internet. We find that there are strong signatures in these networks of topography and use patterns, giving the networks shapes that are quite distinct from one another and from non-geographic networks. We offer an explanation of these differences in terms of the costs and benefits of transportation and communication, and give a simple model based on the Monte Carlo optimization of these costs and benefits that reproduces well the qualitative features of the networks studied.", "The rapid worldwide spread of severe acute respiratory syndrome demonstrated the potential threat an infectious disease poses in a closely interconnected and interdependent world. Here we introduce a probabilistic model that describes the worldwide spread of infectious diseases and demonstrate that a forecast of the geographical spread of epidemics is indeed possible. This model combines a stochastic local infection dynamics among individuals with stochastic transport in a worldwide network, taking into account national and international civil aviation traffic. Our simulations of the severe acute respiratory syndrome outbreak are in surprisingly good agreement with published case reports. We show that the high degree of predictability is caused by the strong heterogeneity of the network. Our model can be used to predict the worldwide spread of future infectious diseases and to identify endangered regions in advance. The performance of different control strategies is analyzed, and our simulations show that a quick and focused reaction is essential to inhibiting the global spread of epidemics.", "We analyze the global structure of the worldwide air transportation network, a critical infrastructure with an enormous impact on local, national, and international economies. We find that the worldwide air transportation network is a scale-free small-world network. In contrast to the prediction of scale-free network models, however, we find that the most connected cities are not necessarily the most central, resulting in anomalous values of the centrality. We demonstrate that these anomalies arise because of the multicommunity structure of the network. We identify the communities in the air transportation network and show that the community structure cannot be explained solely based on geographical constraints and that geopolitical considerations have to be taken into account. We identify each city's global role based on its pattern of intercommunity and intracommunity connections, which enables us to obtain scale-specific representations of the network.", "Networked structures arise in a wide array of different contexts such as technological and transportation infrastructures, social phenomena, and biological systems. These highly interconnected systems have recently been the focus of a great deal of attention that has uncovered and characterized their topological complexity. Along with a complex topological structure, real networks display a large heterogeneity in the capacity and intensity of the connections. These features, however, have mainly not been considered in past studies where links are usually represented as binary states, i.e., either present or absent. Here, we study the scientific collaboration network and the world-wide air-transportation network, which are representative examples of social and large infrastructure systems, respectively. In both cases it is possible to assign to each edge of the graph a weight proportional to the intensity or capacity of the connections among the various elements of the network. We define appropriate metrics combining weighted and topological observables that enable us to characterize the complex statistical properties and heterogeneity of the actual strength of edges and vertices. This information allows us to investigate the correlations among weighted quantities and the underlying topological structure of the network. These results provide a better description of the hierarchies and organizational principles at the basis of the architecture of weighted networks." ] }

{ "cite_N": [ "@cite_0" ], "mid": [ "2139284310" ], "abstract": [ "A mobile ad hoc network consists of mobile nodes that can move freely in an open environment. Communicating nodes in a wireless and mobile ad hoc network usually seek the help of other intermediate nodes to establish communication channels. In such an open environment, malicious intermediate nodes can be a threat to the security and or anonymity of the exchanged data between the mobile nodes. While data encryption can protect the content exchanged between nodes, routing information may reveal valuable information about end users and their relationships. The main purposes of this paper are to study the possibility of achieving anonymity in ad hoc networks, and propose an anonymous routing protocol, similar to onion routing concept used in wired networks. Our protocol includes a mechanism to establish a trust among mobile nodes while avoiding untrustworthy nodes during the route discovery process. The major objective of our protocol is to allow only trustworthy intermediate nodes to participate in the routing protocol without jeopardizing the anonymity of the communicating nodes. We present our scheme, and report on its performance using an extensive set of simulation set of experiments using ns-2 simulator. Our results indicate clearly that anonymity can be achieved in mobile ad hoc networks, and the additional overhead of our scheme to DSR is reasonably low when compared to a non-secure DSR ad hoc routing protocol." ] }

{ "cite_N": [ "@cite_13", "@cite_19", "@cite_1", "@cite_4" ], "mid": [ "1855767844", "118562019", "1482916605", "2071198236" ], "abstract": [ "Mobile agents have recently started being deployed in large-scale distributed systems. However, this new technology brings some security concerns of its own. In this work, we propose a security scheme for protecting mobile agent platforms in large-scale systems. This scheme comprises a mutual authentication protocol for the platforms involved, a mobile agent authenticator, and a method for generation of protection domains. It is based on SPKI SDSI chains of trust, and takes advantage of the flexibility of the SPKI SDSI certificate delegation infrastructure to provide decentralized authorization and authentication control.", "Mobile agent technology offers a new computing paradigm in which a program, in the form of a software agent, can suspend its execution on a host computer, transfer itself to another agent-enabled host on the network, and resume execution on the new host. The use of mobile code has a long history dating back to the use of remote job entry systems in the 1960's. Today's agent incarnations can be characterized in a number of ways ranging from simple distributed objects to highly organized software with embedded intelligence. As the sophistication of mobile software has increased over time, so too have the associated threats to security. This report provides an overview of the range of threats facing the designers of agent platforms and the developers of agentbased applications. The report also identifies generic security objectives, and a range of measures for countering the identified threats and fulfilling these security objectives.", "New portable computers and wireless communication technologies have significantly enhanced mobile computing. The emergence of network technology that supports user mobility and universal network access has prompted new requirements and concerns, especially in the aspects of access control and security. In this paper, we propose a new approach using authorisation agents for cross-domain access control in a mobile computing environment. Our framework consists of three main components, namely centralised authorisation servers, authorisation tokens and authorisation agents. An infrastructure of centralised authorisation servers and application servers from different domains is proposed for supporting trust propagation to mobile hosts instantaneously. While the authorisation token is a form of static capability, the authorisation agent on the client side can be regarded as a dynamic capability to provide the functionality in client-server interactions. It works collaboratively with remote servers to provide authorisation service with finer access granularity and higher flexibility.", "In mobile agent systems, program code together with some process state can autonomously migrate to new hosts. Despite its many practical benefits, mobile agent technology results in significant new security threats from malicious agents and hosts. In this paper, we propose a security architecture to achieve three goals: certification that a server has the authority to execute an agent on behalf of its sender; flexible selection of privileges, so that an agent arriving at a server may be given the privileges necessary to carry out the task for which it has come to the server; and state appraisal, to ensure that an agent has not become malicious as a consequence of alterations to its state. The architecture models the trust relations between the principals of mobile agent systems and includes authentication and authorization mechanisms." ] }

{ "cite_N": [ "@cite_3" ], "mid": [ "2165210192" ], "abstract": [ "A credential system is a system in which users can obtain credentials from organizations and demonstrate possession of these credentials. Such a system is anonymous when transactions carried out by the same user cannot be linked. An anonymous credential system is of significant practical relevance because it is the best means of providing privacy for users. In this paper we propose a practical anonymous credential system that is based on the strong RSA assumption and the decisional Diffie-Hellman assumption modulo a safe prime product and is considerably superior to existing ones: (1) We give the first practical solution that allows a user to unlinkably demonstrate possession of a credential as many times as necessary without involving the issuing organization. (2) To prevent misuse of anonymity, our scheme is the first to offer optional anonymity revocation for particular transactions. (3) Our scheme offers separability: all organizations can choose their cryptographic keys independently of each other. Moreover, we suggest more effective means of preventing users from sharing their credentials, by introducing all-or-nothing sharing: a user who allows a friend to use one of her credentials once, gives him the ability to use all of her credentials, i.e., taking over her identity. This is implemented by a new primitive, called circular encryption, which is of independent interest, and can be realized from any semantically secure cryptosystem in the random oracle model." ] }

{ "cite_N": [ "@cite_5" ], "mid": [ "1992812527" ], "abstract": [ "In this paper we construct a theory of generalized solutions in the large of Cauchy's problem for the equations in the class of bounded measurable functions. We define the generalized solution and prove existence, uniqueness and stability theorems for this solution. To prove the existence theorem we apply the \"vanishing viscosity method\"; in this connection, we first study Cauchy's problem for the corresponding parabolic equation, and we derive a priori estimates of the modulus of continuity in of the solution of this problem which do not depend on small viscosity.Bibliography: 22 items." ] }

{ "cite_N": [ "@cite_5", "@cite_26", "@cite_32" ], "mid": [ "1992812527", "", "205360716" ], "abstract": [ "In this paper we construct a theory of generalized solutions in the large of Cauchy's problem for the equations in the class of bounded measurable functions. We define the generalized solution and prove existence, uniqueness and stability theorems for this solution. To prove the existence theorem we apply the \"vanishing viscosity method\"; in this connection, we first study Cauchy's problem for the corresponding parabolic equation, and we derive a priori estimates of the modulus of continuity in of the solution of this problem which do not depend on small viscosity.Bibliography: 22 items.", "", "Publisher Summary This chapter provides an overview of shock waves and entropy. It describes systems of the first order partial differential equations in conservation form: ∂ t U + ∂ X F = 0, F = F(u). In many cases, all smooth solutions of the first order partial differential equations in conservation form satisfy an additional conservation law where U is a convex function of u. The chapter discusses that for all weak solutions of ∂ t u j +∂ x f j = 0, j=1,…, m, f j =f j (u 1 ,…, u m ), which are limits of solutions of modifications ∂ t u j +∂ x f j = 0, j=1,…, m, f j =f j (u 1 ,…, u m ) , by the introduction of various kinds of dissipation, satisfy the entropy inequality, that is, ∂ t U + ∂ x F≦ 0. The chapter also explains that for weak solutions, which contain discontinuities of moderate strength, ∂ t U + ∂ x F≦ 0 is equivalent to the usual shock condition involving the number of characteristics impinging on the shock. The chapter also describes all possible entropy conditions of ∂ t U + ∂ x F≦ 0 that can be associated to a given hyperbolic system of two conservation laws." ] }

{ "cite_N": [ "@cite_28" ], "mid": [ "1532515344" ], "abstract": [ "Keywords: ecoulement : compressible ; ecoulement : supersonique ; onde de : choc Reference Record created on 2005-11-18, modified on 2016-08-08" ] }

{ "cite_N": [ "@cite_12" ], "mid": [ "2167951823" ], "abstract": [ "■ Abstract Sociologists often model social processes as interactions among variables. We review an alternative approach that models social life as interactions among adaptive agents who influence one another in response to the influence they receive. These agent-based models (ABMs) show how simple and predictable local interactions can generate familiar but enigmatic global patterns, such as the diffusion of information, emergence of norms, coordination of conventions, or participation in collective action. Emergent social patterns can also appear unexpectedly and then just as dramatically transform or disappear, as happens in revolutions, market crashes, fads, and feeding frenzies. ABMs provide theoretical leverage where the global patterns of interest are more than the aggregation of individual attributes, but at the same time, the emergent pattern cannot be understood without a bottom up dynamical model of the microfoundations at the relational level. We begin with a brief historical sketch of the shift from “factors” to “actors” in computational sociology that shows how agent-based modeling differs fundamentally from earlier sociological uses of computer simulation. We then review recent contributions focused on the emergence of social structure and social order out of local interaction. Although sociology has lagged behind other social sciences in appreciating this new methodology, a distinctive sociological contribution is evident in the papers we review. First, theoretical interest focuses on dynamic social networks that shape and are shaped by agent interaction. Second, ABMs are used to perform virtual experiments that test macrosociological theories by manipulating structural factors like network topology, social stratification, or spatial mobility. We conclude our review with a series of recommendations for realizing the rich sociological potential of this approach." ] }

{ "cite_N": [ "@cite_29", "@cite_15", "@cite_8" ], "mid": [ "2011124182", "342706626", "" ], "abstract": [ "A novel logic program like language, weight constraint rules, is developed for answer set programming purposes. It generalizes normal logic programs by allowing weight constraints in place of literals to represent, e.g., cardinality and resource constraints and by providing optimization capabilities. A declarative semantics is developed which extends the stable model semantics of normal programs. The computational complexity of the language is shown to be similar to that of normal programs under the stable model semantics. A simple embedding of general weight constraint rules to a small subclass of the language called basic constraint rules is devised. An implementation of the language, the SMODELS system, is developed based on this embedding. It uses a two level architecture consisting of a front-end and a kernel language implementation. The front-end allows restricted use of variables and functions and compiles general weight constraint rules to basic constraint rules. A major part of the work is the development of an efficient search procedure for computing stable models for this kernel language. The procedure is compared with and empirically tested against satisfiability checkers and an implementation of the stable model semantics. It offers a competitive implementation of the stable model semantics for normal programs and attractive performance for problems where the new types of rules provide a compact representation.", "Aggregates are functions that take sets as arguments. Examples are the function that maps a set to the number of its elements or the function which maps a set to its minimal element. Aggregates are frequently used in relational databases and have many applications in combinatorial search problems and knowledge representation. Aggregates are of particular importance for several extensions of logic programming which are used for declarative programming like Answer Set Programming, Abductive Logic Programming, and the logic of inductive definitions (ID-Logic). Aggregate atoms not only allow a broader class of problems to be represented in a natural way but also allow a more compact representation of problems which often leads to faster solving times. Extensions of specific semantics of logic programs with, in many cases, specific aggregate relations have been proposed before. The main contributions of this thesis are: (i) we extend all major semantics of logic programs: the least model semantics of definite logic programs, the standard model semantics of stratified programs, the Clark completion semantics, the well-founded semantics, the stable models semantics, and the three-valued stable semantics; (ii) our framework admits arbitrary aggregate relations in the bodies of rules. We follow a denotational approach in which a semantics is defined as a (set of) fixpoint(s) of an operator associated with a program. The main tool of this work is Approximation Theory. This is an algebraic theory which defines different types of fixpoints of an approximating operator associated with a logic program. All major semantics of a logic program correspond to specific types of fixpoints of an approximating operator introduced by Fitting. We study different approximating operators for aggregate programs and investigate the precision and complexity of the semantics generated by them. We study in detail one specific operator which extends the Fitting operator and whose semantics extends the three-valued stable semantics of logic programs without aggregates. We look at algorithms, complexity, transformations of aggregate atoms and programs, and an implementation in XSB Prolog.", "" ] }

{ "cite_N": [ "@cite_20", "@cite_10", "@cite_23" ], "mid": [ "1540263588", "1638553575", "1854994931" ], "abstract": [ "We investigate a generalization of weight-constraint programs with stable semantics, as implemented in the ASP solver smodels. Our programs admit atoms of the form ( X, F ) where X is a finite set of propositional atoms and ( F ) is an arbitrary family of subsets of X. We call such atoms set constaints and show that the concept of stable model can be generalized to programs admitting set constraints both in the bodies and the heads of clauses. Natural tools to investigate the fixpoint semantics for such programs are nondeterministic operators in complete lattices. We prove two fixpoint theorems for such operators.", "We investigate mca-programs, that is, logic programs with clauses built of monotone cardinality atoms of the form kX, where k is a non-negative integer and X is a finite set of propositional atoms. We develop a theory of mca-programs. We demonstrate that the operational concept of the one-step provability operator generalizes to mca-programs, but the generalization involves nondeterminism. Our main results show that the formalism of mca-programs is a common generalization of (1) normal logic programming with its semantics of models, supported models and stable models, (2) logic programming with cardinality atoms and with the semantics of stable models, as defined by Niemela, Simons and Soininen, and (3) of disjunctive logic programming with the possible-model semantics of Sakama and Inoue.", "We propose and study extensions of logic programming with constraints represented as generalized atoms of the form C(X), where X is a finite set of atoms and C is an abstract constraint (formally, a collection of sets of atoms). Atoms C(X) are satisfied by an interpretation (set of atoms) M, if M ∩ X ∈ C. We focus here on monotone constraints, that is, those collections C that are closed under the superset. They include, in particular, weight (or pseudo-boolean) constraints studied both by the logic programming and SAT communities. We show that key concepts of the theory of normal logic programs such as the one-step provability operator, the semantics of supported and stable models, as well as several of their properties including complexity results, can be lifted to such case." ] }

{ "cite_N": [ "@cite_27" ], "mid": [ "2105869173" ], "abstract": [ "The addition of aggregates has been one of the most relevant enhancements to the language of answer set programming (ASP). They strengthen the modeling power of ASP, in terms of concise problem representations. While many important problems can be encoded using nonrecursive aggregates, some relevant examples lend themselves for the use of recursive aggregates. Previous semantic definitions typically agree in the nonrecursive case, but the picture is less clear for recursion. Some proposals explicitly avoid recursive aggregates, most others differ, and many of them do not satisfy desirable criteria, such as minimality or coincidence with answer sets in the aggregate-free case." ] }

{ "cite_N": [ "@cite_6" ], "mid": [ "1871606885" ], "abstract": [ "Error correction for polynomial block codes is achieved without prior evaluation of power sum symmetric functions. The received word R (z) is reduced mod G (z), the generator of the code and a function F (z) of error locator polynomial W(z), errata values Y and code dependent functions f(xi) of the error positions xi given by ##EQU1## is decomposed into a rational polynomial function N (z) W (z) for which deg (N (z) )<deg ( W (z) )<number of correctable errors. W (z) is the error locator polynomial, the roots of which are the errata locations X and Y, the correction to the received character is obtained from ##EQU2## evaluated at Xi using non-erased check symbols of R (z). Correction is carried out in a crossbar switch structure which recalls a stored copy of R (z) and corrects bits as specified by (Xi, Yi). Another embodiment interposes a matrix transform to transform the symbols of the received word so as to treat a selected set of symbols as erased checks and to present error location corrections directly to the crossbar. Only when changes occur in the pattern of errata is this error corrector apparatus required to operate and to redetermine the transform executed on incoming data R (z)." ] }

{ "cite_N": [ "@cite_1" ], "mid": [ "2130539706" ], "abstract": [ "For an error-correcting code and a distance bound, the list decoding problem is to compute all the codewords within a given distance to a received message. The bounded distance decoding problem is to find one codeword if there is at least one codeword within the given distance, or to output the empty set if there is not. Obviously the bounded distance decoding problem is not as hard as the list decoding problem. For a Reed-Solomon code [n, k] sup q , a simple counting argument shows that for any integer 0 0. We show that the discrete logarithm problem over F sub qh can be efficiently reduced by a randomized algorithm to the bounded distance decoding problem of the Reed-Solomon code [q, g - h] sub q with radius q - g. These results show that the decoding problems for the Reed-Solomon code are at least as hard as the discrete logarithm problem over finite fields. The main tools to obtain these results are an interesting connection between the problem of list-decoding of Reed-Solomon code and the problem of discrete logarithm over finite fields, and a generalization of Katz's theorem on representations of elements in an extension finite field by products of distinct linear factors." ] }

{ "cite_N": [ "@cite_5", "@cite_15", "@cite_8" ], "mid": [ "1975804880", "2002169759", "2160494326" ], "abstract": [ "Wireless Local Area Networks (WLANs) are now commonplace on many academic and corporate campuses. As \"Wi-Fi\" technology becomes ubiquitous, it is increasingly important to understand trends in the usage of these networks.This paper analyzes an extensive network trace from a mature 802.11 WLAN, including more than 550 access points and 7000 users over seventeen weeks. We employ several measurement techniques, including syslogs, telephone records, SNMP polling and tcpdump packet sniffing. This is the largest WLAN study to date, and the first to look at a large, mature WLAN and consider geographic mobility. We compare this trace to a trace taken after the network's initial deployment two years ago.We found that the applications used on the WLAN changed dramatically. Initial WLAN usage was dominated by Web traffic; our new trace shows significant increases in peer-to-peer, streaming multimedia, and voice over IP (VoIP) traffic. On-campus traffic now exceeds off-campus traffic, a reversal of the situation at the WLAN's initial deployment. Our study indicates that VoIP has been used little on the wireless network thus far, and most VoIP calls are made on the wired network. Most calls last less than a minute.We saw greater heterogeneity in the types of clients used, with more embedded wireless devices such as PDAs and mobile VoIP clients. We define a new metric for mobility, the \"session diameter.\" We use this metric to show that embedded devices have different mobility characteristics than laptops, and travel further and roam to more access points. Overall, users were surprisingly non-mobile, with half remaining close to home about 98 of the time.", "In this paper, we analyze the mobility patterns of users of wireless hand-held PDAs in a campus wireless network using an eleven week trace of wireless network activity. Our study has two goals. First, we characterize the high-level mobility and access patterns of hand-held PDA users and compare these characteristics to previous workload mobility studies focused on laptop users. Second, we develop two wireless network topology models for use in wireless mobility studies: an evolutionary topology model based on user proximity and a campus waypoint model that serves as a trace-based complement to the random waypoint model. We use our evolutionary topology model as a case study for preliminary evaluation of three ad hoc routing algorithms on the network topologies created by the access and mobility patterns of users of modern wireless PDAs. Based upon the mobility characteristics of our trace-based campus waypoint model, we find that commonly parameterized synthetic mobility models have overly aggressive mobility characteristics for scenarios where user movement is limited to walking. Mobility characteristics based on realistic models can have significant implications for evaluating systems designed for mobility. When evaluated using our evolutionary topology model, for example, popular ad hoc routing protocols were very successful at adapting to user mobility, and user mobility was not a key factor in their performance.", "Wireless local-area networks are becoming increasingly popular. They are commonplace on university campuses and inside corporations, and they have started to appear in public areas [17]. It is thus becoming increasingly important to understand user mobility patterns and network usage characteristics on wireless networks. Such an understanding would guide the design of applications geared toward mobile environments (e.g., pervasive computing applications), would help improve simulation tools by providing a more representative workload and better user mobility models, and could result in a more effective deployment of wireless network components.Several studies have recently been performed on wire-less university campus networks and public networks. In this paper, we complement previous research by presenting results from a four week trace collected in a large corporate environment. We study user mobility patterns and introduce new metrics to model user mobility. We also analyze user and load distribution across access points. We compare our results with those from previous studies to extract and explain several network usage and mobility characteristics.We find that average user transfer-rates follow a power law. Load is unevenly distributed across access points and is influenced more by which users are present than by the number of users. We model user mobility with persistence and prevalence. Persistence reflects session durations whereas prevalence reflects the frequency with which users visit various locations. We find that the probability distributions of both measures follow power laws." ] }

{ "cite_N": [ "@cite_8", "@cite_3", "@cite_11" ], "mid": [ "2160494326", "2127484926", "2133436197" ], "abstract": [ "Wireless local-area networks are becoming increasingly popular. They are commonplace on university campuses and inside corporations, and they have started to appear in public areas [17]. It is thus becoming increasingly important to understand user mobility patterns and network usage characteristics on wireless networks. Such an understanding would guide the design of applications geared toward mobile environments (e.g., pervasive computing applications), would help improve simulation tools by providing a more representative workload and better user mobility models, and could result in a more effective deployment of wireless network components.Several studies have recently been performed on wire-less university campus networks and public networks. In this paper, we complement previous research by presenting results from a four week trace collected in a large corporate environment. We study user mobility patterns and introduce new metrics to model user mobility. We also analyze user and load distribution across access points. We compare our results with those from previous studies to extract and explain several network usage and mobility characteristics.We find that average user transfer-rates follow a power law. Load is unevenly distributed across access points and is influenced more by which users are present than by the number of users. We model user mobility with persistence and prevalence. Persistence reflects session durations whereas prevalence reflects the frequency with which users visit various locations. We find that the probability distributions of both measures follow power laws.", "The simulation of mobile networks calls for a mobility model to generate the trajectories of the mobile users (or nodes). It has been shown that the mobility model has a major influence on the behavior of the system. Therefore, using a realistic mobility model is important if we want to increase the confidence that simulations of mobile systems are meaningful in realistic settings. In this paper we present an executable mobility model that uses real-life mobility characteristics to generate mobility scenarios that can be used for network simulations. We present a structured framework for extracting the mobility characteristics from a WLAN trace, for processing the mobility characteristics to determine a parameter set for the mobility model, and for using a parameter set to generate mobility scenarios for simulations. To derive the parameters of the mobility' model, we measure the mobility' characteristics of users of a campus wireless network. Therefore, we call this model the WLAN mobility model Mobility-analysis confirms properties observed by other research groups. The validation shows that the WLAN model maps the real-world mobility' characteristics to the abstract world of network simulators with a very small error. For users that do not have the possibility to capture a WLAN trace, we explore the value space of the WLAN model parameters and show how different parameters sets influence the mobility of the simulated nodes.", "Several studies have recently been performed on wireless university campus networks, corporate and public networks. Yet little is known about the flow-level characterization in such networks. In this paper, we statistically characterize both static flows and roaming flows in a large campus wireless network using a recently-collected trace. For static flows, we take a two-tier approach to characterizing the flow arrivals, which results a Weibull regression model. We further discover that the static flow arrivals in spatial proximity show strong similarity. As for roaming flows, they can also be well characterized statistically.We explain the results by user behaviors and application demands, and further cross-validate the modeling results by three other traces. Finally, we use two examples to illustrate how to apply our models for performance evaluation in the wireless context." ] }

{ "cite_N": [ "@cite_9" ], "mid": [ "2148135143" ], "abstract": [ "In the performance evaluation of a protocol for an ad hoc network, the protocol should be tested under realistic conditions including, but not limited to, a sensible transmission range, limited buffer space for the storage of messages, representative data traffic models, and realistic movements of the mobile users (i.e., a mobility model). This paper is a survey of mobility models that are used in the simulations of ad hoc networks. We describe several mobility models that represent mobile nodes whose movements are independent of each other (i.e., entity mobility models) and several mobility models that represent mobile nodes whose movements are dependent on each other (i.e., group mobility models). The goal of this paper is to present a number of mobility models in order to offer researchers more informed choices when they are deciding upon a mobility model to use in their performance evaluations. Lastly, we present simulation results that illustrate the importance of choosing a mobility model in the simulation of an ad hoc network protocol. Specifically, we illustrate how the performance results of an ad hoc network protocol drastically change as a result of changing the mobility model simulated." ] }

{ "cite_N": [ "@cite_37", "@cite_33", "@cite_50", "@cite_15" ], "mid": [ "1997420616", "2020138862", "2141088850", "2154595228" ], "abstract": [ "Planning for extended goals in non-deterministic domains is one of the most significant and challenging planning problems. In spite of the recent results in this field, no work has proposed a language designed specifically for planning. As a consequence, it is still impossible to specify and plan for several classes of goals that are typical of real world applications, like for instance \"try to achieve a goal whenever possible\", or \"if you fail to achieve a goal, recover by trying to achieve something else\".We propose a new goal language that allows for capturing the intended meaning of these goals. We give a semantics to this language that is radically different from the usual semantics for extended goals, e.g., the semantics for LTL or CTL. Finally, we implement an algorithm for planning for extended goals expressed in this language, and experiment with it on a parametric domain.", "This paper shows how action theories, expressed in an extended version of the language , can be naturally encoded using Prioritized Default Theory. We also show how prioritized default theory can be extended to express preferences between rules. This extension provides a natural framework to introduce different types of preferences in action theories—preferences between actions and preferences between final states. In particular, we demonstrate how these preferences can be expressed within extended prioritized default theory. We also discuss how this framework can be implemented in terms of answer set programming.", "Over the years increasingly sophisticated planning algorithms have been developed. These have made for more efficient planners, but unfortunately these planners still suffer from combinatorial complexity even in simple domains. Theoretical results demonstrate that planning is in the worst case intractable. Nevertheless, planning in particular domains can often be made tractable by utilizing additional domain structure. In fact, it has long been acknowledged that domain independent planners need domain dependent information to help them plan effectively. In this work we present an approach for representing and utilizing domain specific control knowledge. In particular, we show how domain dependent search control knowledge can be represented in a temporal logic, and then utilized to effectively control a forward-chaining planner. There are a number of advantages to our approach, including a declarative semantics for the search control knowledge; a high degree of modularity (new search control knowledge can be added without affecting previous control knowledge); and an independence of this knowledge from the details of the planning algorithm. We have implemented our ideas in the TLPLAN system, and have been able to demonstrate its remarkable effectiveness in a wide range of planning domains.", "In this article we consider three different kinds of domain-dependent control knowledge (temporal, procedural and HTN-based) that are useful in planning. Our approach is declarative and relies on the language of logic programming with answer set semantics (AnsProlog*). AnsProlog* is designed to plan without control knowledge. We show how temporal, procedural and HTN-based control knowledge can be incorporated into AnsProlog* by the modular addition of a small number of domain-dependent rules, without the need to modify the planner. We formally prove the correctness of our planner, both in the absence and presence of the control knowledge. Finally, we perform some initial experimentation that demonstrates the potential reduction in planning time that can be achieved when procedural domain knowledge is used to solve planning problems with large plan length." ] }

{ "cite_N": [ "@cite_3" ], "mid": [ "1633032608" ], "abstract": [ "Recently, planning based on answer set programming has been proposed as an approach towards realizing declarative planning systems. In this paper, we present the language κc, which extends the declarative planning language κ by action costs. κc provides the notion of admissible and optimal plans, which are plans whose overall action costs are within a given limit resp. minimum over all plans (i.e., cheapest plans). As we demonstrate, this novel language allows for expressing some nontrivial planning tasks in a declarative way. Furthermore, it can be utilized for representing planning problems under other optimality criteria, such as computing \"shortest\" plans (with the least number of steps), and refinement combinations of cheapest and fastest plans. We study complexity aspects of the language κc and provide a transformation to logic programs, such that planning problems are solved via answer set programming. Furthermore, we report experimental results on selected problems. Our experience is encouraging that answer set planning may be a valuable approach to expressive planning systems in which intricate planning problems can be naturally specified and solved." ] }

{ "cite_N": [ "@cite_18", "@cite_26", "@cite_36", "@cite_28", "@cite_27", "@cite_23", "@cite_47" ], "mid": [ "2174235632", "2011124182", "", "1563821244", "1986318362", "2124627636", "2106614716" ], "abstract": [ "We introduce a methodology and framework for expressing general preference information in logic programming under the answer set semantics. An ordered logic program is an extended logic program in which rules are named by unique terms, and in which preferences among rules are given by a set of atoms of form s p t where s and t are names. An ordered logic program is transformed into a second, regular, extended logic program wherein the preferences are respected, in that the answer sets obtained in the transformed program correspond with the preferred answer sets of the original program. Our approach allows the specification of dynamic orderings, in which preferences can appear arbitrarily within a program. Static orderings (in which preferences are external to a logic program) are a trivial restriction of the general dynamic case. First, we develop a specific approach to reasoning with preferences, wherein the preference ordering specifies the order in which rules are to be applied. We then demonstrate the wide range of applicability of our framework by showing how other approaches, among them that of Brewka and Eiter, can be captured within our framework. Since the result of each of these transformations is an extended logic program, we can make use of existing implementations, such as dlv and smodels. To this end, we have developed a publicly available compiler as a front-end for these programming systems.", "A novel logic program like language, weight constraint rules, is developed for answer set programming purposes. It generalizes normal logic programs by allowing weight constraints in place of literals to represent, e.g., cardinality and resource constraints and by providing optimization capabilities. A declarative semantics is developed which extends the stable model semantics of normal programs. The computational complexity of the language is shown to be similar to that of normal programs under the stable model semantics. A simple embedding of general weight constraint rules to a small subclass of the language called basic constraint rules is devised. An implementation of the language, the SMODELS system, is developed based on this embedding. It uses a two level architecture consisting of a front-end and a kernel language implementation. The front-end allows restricted use of variables and functions and compiles general weight constraint rules to basic constraint rules. A major part of the work is the development of an efficient search procedure for computing stable models for this kernel language. The procedure is compared with and empirically tested against satisfiability checkers and an implementation of the stable model semantics. It offers a competitive implementation of the stable model semantics for normal programs and attractive performance for problems where the new types of rules provide a compact representation.", "", "We are interested in semantical underpinnings for existing approaches to preference handling in extended logic programming (within the framework of answer set programming). As a starting point, we explore three different approaches that have been recently proposed in the literature. Because these approaches use rather different formal means, we furnish a series of uniform characterizations that allow us to gain insights into the relationships among these approaches. To be more precise, we provide different characterizations in terms of (i) fixpoints, (ii) order preservation, and (iii) translations into standard logic programs. While the two former provide semantics for logic programming with preference information, the latter furnishes implementation techniques for these approaches.", "The addition of preferences to normal logic programs is a convenient way to represent many aspects of default reasoning. If the derivation of an atom A1 is preferred to that of an atom A2, a preference rule can be defined so that A2 is derived only if A1 is not. Although such situations can be modelled directly using default negation, it is often easier to define preference rules than it is to add negation to the bodies of rules. As first noted by [Proc. Internat. Conf. on Logic Programming, 1995, pp. 731-746], for certain grammars, it may be easier to disambiguate parses using preferences than by enforcing disambiguation in the grammar rules themselves. In this paper we define a general fixed-point semantics for preference logic programs based on an embedding into the well-founded semantics, and discuss its features and relation to previous preference logic semantics. We then study how preference logic grammars are used in data standardization, the commercially important process of extracting useful information from poorly structured textual data. This process includes correcting misspellings and truncations that occur in data, extraction of relevant information via parsing, and correcting inconsistencies in the extracted information. The declarativity of Prolog offers natural advantages for data standardization, and a commercial standardizer has been implemented using Prolog. However, we show that the use of preference logic grammars allow construction of a much more powerful and declarative commercial standardizer, and discuss in detail how the use of the non-monotonic construct of preferences leads to improved commercial software.", "Abstract In this paper, we address the issue of how Gelfond and Lifschitz's answer set semantics for extended logic programs can be suitably modified to handle prioritized programs. In such programs an ordering on the program rules is used to express preferences. We show how this ordering can be used to define preferred answer sets and thus to increase the set of consequences of a program. We define a strong and a weak notion of preferred answer sets. The first takes preferences more seriously, while the second guarantees the existence of a preferred answer set for programs possessing at least one answer set. Adding priorities to rules is not new, and has been explored in different contexts. However, we show that many approaches to priority handling, most of which are inherited from closely related formalisms like default logic, are not suitable and fail on intuitive examples. Our approach, which obeys abstract, general principles that any approach to prioritized knowledge representation should satisfy, handles them in the expected way. Moreover, we investigate the complexity of our approach. It appears that strong preference on answer sets does not add on the complexity of the principal reasoning tasks, and weak preference leads only to a mild increase in complexity.", "This paper presents an extension of Disjunctive Datalog (DATALOG sup V, spl sim ) by integrity constraints. These are of two types: strong, that is, classical integrity constraints and weak, that is, constraints that are satisfied if possible. While strong constraints must be satisfied, weak constraints express desiderata, that is, they may be violated-actually, their semantics tends to minimize the number of violated instances of weak constraints. Weak constraints may be ordered according to their importance to express different priority levels. As a result, the proposed language (call it, DATALOG sup V, spl sim ,c ) is well-suited to represent common sense reasoning and knowledge-based problems arising in different areas of computer science such as planning, graph theory optimizations, and abductive reasoning. The formal definition of the language is first given. The declarative semantics of DATALOG sup V, spl sim ,c is defined in a general way that allows us to put constraints on top of any existing (model-theoretic) semantics for DATALOG sup V, spl sim programs. Knowledge representation issues are then addressed and the complexity of reasoning on DATALOG sup V, spl sim ,c programs is carefully determined. An in-depth discussion on complexity and expressiveness of DATALOG sup V, spl sim ,c is finally reported. The discussion contrasts DATALOG sup V, spl sim ,c to DATALOG sup V, spl sim and highlights the significant increase in knowledge modeling ability carried out by constraints." ] }

{ "cite_N": [ "@cite_36" ], "mid": [ "2053053770" ], "abstract": [ "Let ƒ, g be measurable non-negative functions on R, and let , ḡ be their equimeasurable symmetric decreasing rearrangements. Let F: R × R → R be continuous and suppose that the associated rectangle function defined by F(R) = F(a, c) + F(b, d) − F(a, d) − F(b, c) for R = [(x, y) ϵ R2¦ a ⩽ x ⩽ b, c ⩽ y ⩽ d], is non-negative. Then ∝ F(ƒ, g) dμ ⩽ ∝ F( , g) dμ, where μ is Lebesgue measure. The concept of equimeasurable rearrangement is also defined for functions on a more general class of measure spaces, and the inequality holds in the general case. If F(x, y) = −ϑ(x − y), where ϑ is convex and ϑ(0) = 0, then we obtain ∝ ϑ( − g) dμ ⩽ ∝ ϑ(ƒ − g) dμ. In particular, if ϑ(x) = ¦x¦p, 1 ⩽ p ⩽ +∞, then we find that the operator S:ƒ → is a contraction on Lp for 1 ⩽ p ⩽ +∞." ] }

{ "cite_N": [ "@cite_35" ], "mid": [ "2183160839" ], "abstract": [ "We prove existence, uniqueness, duality results and give a characterization of optimal measure-preserving maps for a class of optimal transportation problems with several marginals with compact support in R under the requirement that the cost function satisfles a so-called monotonicity of order 2 condition. Explicit formulas for the minimizers are given and links with some rearrangement inequalities are sketched." ] }

{ "cite_N": [ "@cite_26", "@cite_22", "@cite_8", "@cite_9", "@cite_21", "@cite_32", "@cite_0", "@cite_19", "@cite_5", "@cite_15", "@cite_13", "@cite_25" ], "mid": [ "1659004305", "1515452785", "2085996269", "", "1999441752", "", "1988493560", "2157142525", "2066606909", "", "2016665346", "2162337698" ], "abstract": [ "The equation dealt with in this paper is in three dimensions. It comes from minimizing the functional which, in turn, comes from an approximation to the Hartree-Fock theory of a plasma. It describes an electron trapped in its own hole. The interesting mathematical aspect of the problem is that & is not convex, and usual methods to show existence and uniqueness of the minimum do not apply. By using symmetric decreasing rearrangement inequalities we are able to prove existence and uniqueness (modulo translations) of a minimizing Φ. To prove uniqueness a strict form of the inequality, which we believe is new, is employed.", "", "", "", "where de denotes normalized surface measure, V is the conformal gradient and q = (2n) (n 2). A modern folklore theorem is that by taking the infinitedimensional limit of this inequality, one obtains the Gross logarithmic Sobolev inequality for Gaussian measure, which determines Nelson's hypercontractive estimates for the Hermite semigroup (see [8]). One observes using conformal invariance that the above inequality is equivalent to the sharp Sobolev inequality on Rn for which boundedness and extremal functions can be easily calculated using dilation invariance and geometric symmetrization. The roots here go back to Hardy and Littlewood. The advantage of casting the problem on the sphere is that the role of the constants is evident, and one is led immediately to the conjecture that this inequality should hold whenever possible (for example, 2 < q < 0o if n = 2). This is in fact true and will be demonstrated in Section 2. A clear question at this point is \"What is the situation in dimension 2?\" Two important arguments ([25], [26], [27]) dealt with this issue, both motivated by geometric variational problems. Because q goes to infinity for dimension 2, the appropriate function space is the exponential class. Responding in part", "", "We prove rearrangement inequalities for multiple integrals, using the polarization technique. Polarization refers to rearranging a function with respect to a hyperplane. Then we derive sharp inequalities for ratios of integrals of heat kernels of Schrodinger operators, using our polarization inequalities. These ratio inequalities imply inequalities for the partition functions and extend the results of R. Banuelos, P.J. Mendez-Hernandez and D. You.", "", "Method and optical driver aid for following a prescribed simulated motor vehicle driving schedule, for example, such as used in automobile exhaust emission control tests, wherein a moving driving cycle trace is projected onto a viewing screen and followed by an indicator means which is responsive to the motor vehicle speed and operation.", "", "", "We study bounds on the exit time of Brownian motion from a set in terms of its size and shape, and the relation of such bounds with isoperimetric inequalities. The first result is an upper bound for the distribution function of the exit time from a subset of a sphere or hyperbolic space of constant curvature in terms of the exit time from a disc of the same volume. This amounts to a rearrangement inequality for the Dirichlet heat kernel. To connect this inequality with the classical isoperimetric inequality, we derive a formula for the perimeter of a set in terms of the heat flow over the boundary. An auxiliary result generalizes Riesz' rearrangement inequality to multiple integrals." ] }

{ "cite_N": [ "@cite_13", "@cite_1", "@cite_17" ], "mid": [ "", "2139135093", "2008896880" ], "abstract": [ "", "Schema matching is a critical step in many applications, such as XML message mapping, data warehouse loading, and schema integration. In this paper, we investigate algorithms for generic schema matching, outside of any particular data model or application. We first present a taxonomy for past solutions, showing that a rich range of techniques is available. We then propose a new algorithm, Cupid, that discovers mappings between schema elements based on their names, data types, constraints, and schema structure, using a broader set of techniques than past approaches. Some of our innovations are the integrated use of linguistic and structural matching, context-dependent matching of shared types, and a bias toward leaf structure where much of the schema content resides. After describing our algorithm, we present experimental results that compare Cupid to two other schema matching systems.", "Schema matching is a basic problem in many database application domains, such as data integration, E-business, data warehousing, and semantic query processing. In current implementations, schema matching is typically performed manually, which has significant limitations. On the other hand, previous research papers have proposed many techniques to achieve a partial automation of the match operation for specific application domains. We present a taxonomy that covers many of these existing approaches, and we describe the approaches in some detail. In particular, we distinguish between schema-level and instance-level, element-level and structure-level, and language-based and constraint-based matchers. Based on our classification we review some previous match implementations thereby indicating which part of the solution space they cover. We intend our taxonomy and review of past work to be useful when comparing different approaches to schema matching, when developing a new match algorithm, and when implementing a schema matching component." ] }

{ "cite_N": [ "@cite_30", "@cite_19", "@cite_18", "@cite_21" ], "mid": [ "2099849300", "1558940048", "2145290781", "2120176307" ], "abstract": [ "We present the design and evaluation of PeerDB, a peer-to-peer (P2P) distributed data sharing system. PeerDB distinguishes itself from existing P2P systems in several ways. First, it is a full-fledge data management system that supports fine-grain content-based searching. Second, it facilitates sharing of data without shared schema. Third, it combines the power of mobile agents into P2P systems to perform operations at peers' sites. Fourth, PeerDB network is self-configurable, i.e., a node can dynamically optimize the set of peers that it can communicate directly with based on some optimization criterion. By keeping peers that provide most information or services in close proximity (i.e., direct communication), the network bandwidth can be better utilized and system performance can be optimized. We implemented and evaluated PeerDB on a cluster of 32 Pentium II PCs. Our experimental results show that PeerDB can effectively exploit P2P technologies for distributed data sharing.", "In this paper, we address the problem of designing a scalable, accurate query processor for peer-to-peer filesharing and similar distributed keyword search systems. Using a globally-distributed monitoring infrastructure, we perform an extensive study of the Gnutella filesharing network, characterizing its topology, data and query workloads. We observe that Gnutella's query processing approach performs well for popular content, but quite poorly for rare items with few replicas. We then consider an alternate approach based on Distributed Hash Tables (DHTs). We describe our implementation of PIERSearch, a DHT-based system, and propose a hybrid system where Gnutella is used to locate popular items, and PIERSearch for handling rare items. We develop an analytical model of the two approaches, and use it in concert with our Gnutella traces to study the trade-off between query recall and system overhead of the hybrid system. We evaluate a variety of localized schemes for identifying items that are rare and worth handling via the DHT. Lastly, we show in a live deployment on fifty nodes on two continents that it nicely complements Gnutella in its ability to handle rare items.", "We present an architecture for a data sharing peer-to-peer system where the data is shared in the form of database relations. In general, peer-to-peer systems try to locate exactmatch data objects to simple user queries. Since peer-to-peer users generally tend to submit broad queries in order to find data of their interest, we develop a P2P data sharing architecture for computing approximate answers for the complex queries by finding data ranges that are similar to the user query. Thus this paper represents the first step towards solving the general range lookup problem over P2P systems instead of exact lookup operations.", "Querying large numbers of data sources is gaining importance due to increasing numbers of independent data providers. One of the key challenges is executing queries on all relevant information sources in a scalable fashion and retrieving fresh results. The key to scalability is to send queries only to the relevant servers and avoid wasting resources on data sources which will not provide any results. Thus, a catalog service, which would determine the relevant data sources given a query, is an essential component in efficiently processing queries in a distributed environment. This paper proposes a catalog framework which is distributed across the data sources themselves and does not require any central infrastructure. As new data sources become available, they automatically become part of the catalog service infrastructure, which allows scalability to large numbers of nodes. Furthermore, we propose techniques for workload adaptability. Using simulation and real-world data we show that our approach is valid and can scale to thousands of data sources." ] }

{ "cite_N": [ "@cite_10" ], "mid": [ "2000805332" ], "abstract": [ "We define a language for representing context-sensitive probabilistic knowledge. A knowledge base consists of a set of universally quantified probability sentences that include context constraints, which allow inference to be focused on only the relevant portions of the probabilistic knowledge. We provide a declarative semantics for our language. We present a query answering procedure that takes a query Q and a set of evidence E and constructs a Bayesian network to compute P(Q¦E). The posterior probability is then computed using any of a number of Bayesian network inference algorithms. We use the declarative semantics to prove the query procedure sound and complete. We use concepts from logic programming to justify our approach." ] }

{ "cite_N": [ "@cite_3", "@cite_6" ], "mid": [ "1530394184", "2094982166" ], "abstract": [ "Publisher Summary This chapter presents an overview of usability inspection methods. Usability inspection is the generic name for a set of methods based on having evaluators inspect or examine usability-related aspects of a user interface. Usability inspectors can be usability specialists, but they can also be software development consultants with special expertise, end users with content or task knowledge, or other types of professionals. The different inspection methods have slightly different goals, but normally, usability inspection is intended as a way of evaluating user interface designs. In usability inspection, the evaluation of the user interface is based on the considered judgment of the inspector(s). The individual inspection methods vary as to how this judgment is derived and on what evaluative criteria inspectors are expected to base their judgments. Typically, a usability inspection is aimed at finding usability problems in an existing user interface design, and then using these problems to make recommendations for fixing the problems and improving the usability of the design. This means that usability inspections are normally used at the stage in the usability engineering cycle when a user interface design has been generated and its usability for users needs to be evaluated.", "We describe the i-LAND environment which constitutes an exampleof our vision of the workspaces of the future, in this casesupporting cooperative work of dynamic teams with changing needs.i-LAND requires and provides new forms of human-computerinteraction and new forms of computer-supported cooperative work.Its design is based on an integration of information andarchitectural spaces, implications of new work practices and anempirical requirements study informing our design. i-LAND consistsof several roomware components, i.e. computer-aug- mented objectsintegrating room elements with information technology. We presentthe current realization of i-LAND in terms of an interactiveelectronic wall, an interactive table, two computer-enhancedchairs, and two bridges for the Passage-mechanism. This iscomplemented by the description of the creativity supportapplication and the technological infrastructure. The paper isaccompanied by a video figure in the CHI99 video program." ] }

{ "cite_N": [ "@cite_0" ], "mid": [ "2006563349" ], "abstract": [ "We describe the design of and experience with PointRight, a peer-to-peer pointer and keyboard redirection system that operates in multi-machine, multi-user environments. PointRight employs a geometric model for redirecting input across screens driven by multiple independent machines and operating systems. It was created for interactive workspaces that include large, shared displays and individual laptops, but is a general tool that supports many different configurations and modes of use. Although previous systems have provided for re-routing pointer and keyboard control, in this paper we present a more general and flexible system, along with an analysis of the types of re-binding that must be handled by any pointer redirection system This paper describes the system, the ways in which it has been used, and the lessons that have been learned from its use over the last two years." ] }

{ "cite_N": [ "@cite_1" ], "mid": [ "2108715885" ], "abstract": [ "This paper proposes a new field of user interfaces called multi-computer direct manipulation and presents a penbased direct manipulation technique that can be used for data transfer between different computers as well as within the same computer. The proposed Pick-andDrop allows a user to pick up an object on a display and drop it on another display as if he she were manipulating a physical object. Even though the pen itself does not have storage capabilities, a combination of Pen-ID and the pen manager on the network provides the illusion that the pen can physically pick up and move a computer object. Based on this concept, we have built several experimental applications using palm-sized, desk-top, and wall-sized pen computers. We also considered the importance of physical artifacts in designing user interfaces in a future computing environment." ] }

{ "cite_N": [ "@cite_4" ], "mid": [ "2137775453" ], "abstract": [ "When n identical randomly located nodes, each capable of transmitting at W bits per second and using a fixed range, form a wireless network, the throughput spl lambda (n) obtainable by each node for a randomly chosen destination is spl Theta (W spl radic (nlogn)) bits per second under a noninterference protocol. If the nodes are optimally placed in a disk of unit area, traffic patterns are optimally assigned, and each transmission's range is optimally chosen, the bit-distance product that can be transported by the network per second is spl Theta (W spl radic An) bit-meters per second. Thus even under optimal circumstances, the throughput is only spl Theta (W spl radic n) bits per second for each node for a destination nonvanishingly far away. Similar results also hold under an alternate physical model where a required signal-to-interference ratio is specified for successful receptions. Fundamentally, it is the need for every node all over the domain to share whatever portion of the channel it is utilizing with nodes in its local neighborhood that is the reason for the constriction in capacity. Splitting the channel into several subchannels does not change any of the results. Some implications may be worth considering by designers. Since the throughput furnished to each user diminishes to zero as the number of users is increased, perhaps networks connecting smaller numbers of users, or featuring connections mostly with nearby neighbors, may be more likely to be find acceptance." ] }

{ "cite_N": [ "@cite_9", "@cite_4" ], "mid": [ "2162180430", "2137775453" ], "abstract": [ "How much information can be carried over a wireless network with a multiplicity of nodes, and how should the nodes cooperate to transfer information? To study these questions, we formulate a model of wireless networks that particularly takes into account the distances between nodes, and the resulting attenuation of radio signals, and study a performance measure that weights information by the distance over which it is transported. Consider a network with the following features. I) n nodes located on a plane, with minimum separation distance spl rho sub min >0. II) A simplistic model of signal attenuation e sup - spl gamma spl rho spl rho sup spl delta over a distance spl rho , where spl gamma spl ges 0 is the absorption constant (usually positive, unless over a vacuum), and spl delta >0 is the path loss exponent. III) All receptions subject to additive Gaussian noise of variance spl sigma sup 2 . The performance measure we mainly, but not exclusively, study is the transport capacity C sub T :=sup spl Sigma on sub spl lscr =1 sup m R sub spl lscr spl middot spl rho sub spl lscr , where the supremum is taken over m, and vectors (R sub 1 ,R sub 2 ,...,R sub m ) of feasible rates for m source-destination pairs, and spl rho sub spl lscr is the distance between the spl lscr th source and its destination. It is the supremum distance-weighted sum of rates that the wireless network can deliver. We show that there is a dichotomy between the cases of relatively high and relatively low attenuation. When spl gamma >0 or spl delta >3, the relatively high attenuation case, the transport capacity is bounded by a constant multiple of the sum of the transmit powers of the nodes in the network. However, when spl gamma =0 and spl delta <3 2, the low-attenuation case, we show that there exist networks that can provide unbounded transport capacity for fixed total power, yielding zero energy priced communication. Examples show that nodes can profitably cooperate over large distances using coherence and multiuser estimation when the attenuation is low. These results are established by developing a coding scheme and an achievable rate for Gaussian multiple-relay channels, a result that may be of interest in its own right.", "When n identical randomly located nodes, each capable of transmitting at W bits per second and using a fixed range, form a wireless network, the throughput spl lambda (n) obtainable by each node for a randomly chosen destination is spl Theta (W spl radic (nlogn)) bits per second under a noninterference protocol. If the nodes are optimally placed in a disk of unit area, traffic patterns are optimally assigned, and each transmission's range is optimally chosen, the bit-distance product that can be transported by the network per second is spl Theta (W spl radic An) bit-meters per second. Thus even under optimal circumstances, the throughput is only spl Theta (W spl radic n) bits per second for each node for a destination nonvanishingly far away. Similar results also hold under an alternate physical model where a required signal-to-interference ratio is specified for successful receptions. Fundamentally, it is the need for every node all over the domain to share whatever portion of the channel it is utilizing with nodes in its local neighborhood that is the reason for the constriction in capacity. Splitting the channel into several subchannels does not change any of the results. Some implications may be worth considering by designers. Since the throughput furnished to each user diminishes to zero as the number of users is increased, perhaps networks connecting smaller numbers of users, or featuring connections mostly with nearby neighbors, may be more likely to be find acceptance." ] }

{ "cite_N": [ "@cite_4" ], "mid": [ "2137775453" ], "abstract": [ "When n identical randomly located nodes, each capable of transmitting at W bits per second and using a fixed range, form a wireless network, the throughput spl lambda (n) obtainable by each node for a randomly chosen destination is spl Theta (W spl radic (nlogn)) bits per second under a noninterference protocol. If the nodes are optimally placed in a disk of unit area, traffic patterns are optimally assigned, and each transmission's range is optimally chosen, the bit-distance product that can be transported by the network per second is spl Theta (W spl radic An) bit-meters per second. Thus even under optimal circumstances, the throughput is only spl Theta (W spl radic n) bits per second for each node for a destination nonvanishingly far away. Similar results also hold under an alternate physical model where a required signal-to-interference ratio is specified for successful receptions. Fundamentally, it is the need for every node all over the domain to share whatever portion of the channel it is utilizing with nodes in its local neighborhood that is the reason for the constriction in capacity. Splitting the channel into several subchannels does not change any of the results. Some implications may be worth considering by designers. Since the throughput furnished to each user diminishes to zero as the number of users is increased, perhaps networks connecting smaller numbers of users, or featuring connections mostly with nearby neighbors, may be more likely to be find acceptance." ] }

{ "cite_N": [ "@cite_10" ], "mid": [ "1531318324" ], "abstract": [ "The problem of network security is approached from the point of view of Kolmogorov complexity (see Evans. S, et al, Proc. DARPA Inf. Survivability Conf. & Exposition II, vol 2. p.322-33, 2001). The principle of conservation of complexity is utilized to identify healthy complexity norms objectively and detect attacks via deviation of these norms under TCP IP. Observed complexity changes that fall within expected hounds are indicators of system health, while complexity changes outside the expected bounds for normal protocol and application use are indicators of system fault or attack. Experimental results using FTP normal and attack sessions are presented." ] }

{ "cite_N": [ "@cite_7" ], "mid": [ "2005406777" ], "abstract": [ "This paper describes an approach to detecting distributed denial of service (DDoS) attacks that is based on fundamentals of Information Theory, specifically Kolmogorov Complexity. A theorem derived using principles of Kolmogorov Complexity states that the joint complexity measure of random strings is lower than the sum of the complexities of the individual strings when the strings exhibit some correlation. Furthermore, the joint complexity measure varies inversely with the amount of correlation. We propose a distributed active network-based algorithm that exploits this property to correlate arbitrary traffic flows in the network to detect possible denial-of-service attacks. One of the strengths of this algorithm is that it does not require special filtering rules and hence it can be used to detect any type of DDoS attack. We implement and investigate the performance of the algorithm in an active network. Our results show that DDoS attacks can be detected in a manner that is not sensitive to legitimate background traffic." ] }

{ "cite_N": [ "@cite_30" ], "mid": [ "2001834587" ], "abstract": [ "While search engines have become the major decision support tools for the Internet, there is a growing disparity between the image of the World Wide Web stored in search engine repositories and the actual dynamic, distributed nature of Web data. We propose to attack this problem using an adaptive population of intelligent agents mining the Web online at query time. We discuss the benefits and shortcomings of using dynamic search strategies versus the traditional static methods in which search and retrieval are disjoint. This paper presents a public Web intelligence tool called MySpiders, a threaded multiagent system designed for information discovery. The performance of the system is evaluated by comparing its effectiveness in locating recent, relevant documents with that of search engines. We present results suggesting that augmenting search engines with adaptive populations of intelligent search agents can lead to a significant competitive advantage. We also discuss some of the challenges of evaluating such a system on current Web data, introduce three novel metrics for this purpose, and outline some of the lessons learned in the process." ] }

{ "cite_N": [ "@cite_0" ], "mid": [ "2046862025" ], "abstract": [ "Abstract In this paper we study several dimensions of Web dynamics in the context of large-scale Internet search engines. Both growth and update dynamics clearly represent big challenges for search engines. We show how the problems arise in all components of a reference search engine model. Furthermore, we use the FAST Search Engine architecture as a case study for showing some possible solutions for Web dynamics and search engines. The focus is to demonstrate solutions that work in practice for real systems. The service is running live at www.alltheweb.com and major portals worldwide with more than 30 million queries a day, about 700 million full-text documents, a crawl base of 1.8 billion documents, updated every 11 days, at a rate of 400 documents second. We discuss future evolution of the Web, and some important issues for search engines will be scheduling and query execution as well as increasingly heterogeneous architectures to handle the dynamic Web." ] }

{ "cite_N": [ "@cite_30" ], "mid": [ "2001834587" ], "abstract": [ "While search engines have become the major decision support tools for the Internet, there is a growing disparity between the image of the World Wide Web stored in search engine repositories and the actual dynamic, distributed nature of Web data. We propose to attack this problem using an adaptive population of intelligent agents mining the Web online at query time. We discuss the benefits and shortcomings of using dynamic search strategies versus the traditional static methods in which search and retrieval are disjoint. This paper presents a public Web intelligence tool called MySpiders, a threaded multiagent system designed for information discovery. The performance of the system is evaluated by comparing its effectiveness in locating recent, relevant documents with that of search engines. We present results suggesting that augmenting search engines with adaptive populations of intelligent search agents can lead to a significant competitive advantage. We also discuss some of the challenges of evaluating such a system on current Web data, introduce three novel metrics for this purpose, and outline some of the lessons learned in the process." ] }

{ "cite_N": [ "@cite_31" ], "mid": [ "2018928332" ], "abstract": [ "This paper outlines the design of a web crawler implemented for IBM Almaden's WebFountain project and describes an optimization model for controlling the crawl strategy. This crawler is scalable and incremental. The model makes no assumptions about the statistical behaviour of web page changes, but rather uses an adaptive approach to maintain data on actual change rates which are in turn used as inputs for the optimization. Computational results with simulated but realistic data show that there is no magic bullet' different, but equally plausible, objectives lead to con icting optimal' strategies. However, we nd that there are compromise objectives which lead to good strategies that are robust against a number of criteria." ] }

{ "cite_N": [ "@cite_0", "@cite_9", "@cite_30" ], "mid": [ "2046862025", "", "2001834587" ], "abstract": [ "Abstract In this paper we study several dimensions of Web dynamics in the context of large-scale Internet search engines. Both growth and update dynamics clearly represent big challenges for search engines. We show how the problems arise in all components of a reference search engine model. Furthermore, we use the FAST Search Engine architecture as a case study for showing some possible solutions for Web dynamics and search engines. The focus is to demonstrate solutions that work in practice for real systems. The service is running live at www.alltheweb.com and major portals worldwide with more than 30 million queries a day, about 700 million full-text documents, a crawl base of 1.8 billion documents, updated every 11 days, at a rate of 400 documents second. We discuss future evolution of the Web, and some important issues for search engines will be scheduling and query execution as well as increasingly heterogeneous architectures to handle the dynamic Web.", "", "While search engines have become the major decision support tools for the Internet, there is a growing disparity between the image of the World Wide Web stored in search engine repositories and the actual dynamic, distributed nature of Web data. We propose to attack this problem using an adaptive population of intelligent agents mining the Web online at query time. We discuss the benefits and shortcomings of using dynamic search strategies versus the traditional static methods in which search and retrieval are disjoint. This paper presents a public Web intelligence tool called MySpiders, a threaded multiagent system designed for information discovery. The performance of the system is evaluated by comparing its effectiveness in locating recent, relevant documents with that of search engines. We present results suggesting that augmenting search engines with adaptive populations of intelligent search agents can lead to a significant competitive advantage. We also discuss some of the challenges of evaluating such a system on current Web data, introduce three novel metrics for this purpose, and outline some of the lessons learned in the process." ] }

{ "cite_N": [ "@cite_41", "@cite_5", "@cite_14" ], "mid": [ "", "2155218845", "1561608403" ], "abstract": [ "", "Abstract Determining whether a propositional theory is satisfiable is a prototypical example of an NP-complete problem. Further, a large number of problems that occur in knowledge-representation, learning, planning, and other areas of AI are essentially satisfiability problems. This paper reports on the most extensive set of experiments to date on the location and nature of the crossover point in satisfiability problems. These experiments generally confirm previous results with two notable exceptions. First, we have found that neither of the functions previously proposed accurately models the location of the crossover point. Second, we have found no evidence of any hard problems in the under-constrained region. In fact the hardest problems found in the under-constrained region were many times easier than the easiest unsatisfiable problems found in the neighborhood of the crossover point. We offer explanations for these apparent contradictions of previous results.", "Determining whether a propositional theory is satisfiable is a prototypical example of an NP-complete problem. Further, a large number of problems that occur in knowledge representation, learning, planning, and other areas of AI are essentially satisfiability problems. This paper reports on a series of experiments to determine the location of the crossover point -- the point at which half the randomly generated propositional theories with a given number of variables and given number of clauses are satisfiable -- and to assess the relationship of the crossover point to the difficulty of determining satisfiability. We have found empirically that, for 3-SAT, the number of clauses at the crossover point is a linear function of the number of variables. This result is of theoretical interest since it is not clear why such a linear relationship should exist, but it is also of practical interest since recent experiments [ 92; 91] indicate that the most computationally difficult problems tend to be found near the crossover point. We have also found that for random 3-SAT problems below the crossover point, the average time complexity of satisfiability problems seems empirically to grow linearly with problem size. At and above the crossover point the complexity seems to grow exponentially, but the rate of growth seems to be greatest near the crossover point." ] }

{ "cite_N": [ "@cite_30", "@cite_48", "@cite_29", "@cite_21", "@cite_51", "@cite_11" ], "mid": [ "2137154807", "2088616860", "", "2126420408", "2002627038", "" ], "abstract": [ "We present a detailed experimental investigation of the easy-hard-easy phase transition for randomly generated instances of satisfiability problems. Problems in the hard part of the phase transition have been extensively used for benchmarking satisfiability algorithms. This study demonstrates that problem classes and regions of the phase transition previously thought to be easy can sometimes be orders of magnitude more difficult than the worst problems in problem classes and regions of the phase transition considered hard. These difficult problems are either hard unsatisfiable problems or are satisfiable problems which give a hard unsatisfiable subproblem following a wrong split. Whilst these hard unsatisfiable problems may have short proofs, these appear to be difficult to find, and other proofs are long and hard.", "WC study the complexity of proving unsatisfiability for random k-CNP formulas with clause density A = m n where 111 is number of clauses and n is the number of variables. We prove the first nontrivial general upper bound, giving algorithmo that, in particular, for k = 3 produce refutations almost certainly in time 20t”iA). This is polynomial when", "", "For every choice of positive integers c and k such that k ≥ 3 and c 2 - k ≥ 0.7, there is a positive number e such that, with probability tending to 1 as n tends to ∞, a randomly chosen family of cn clauses of size k over n variables is unsatisfiable, but every resolution proof of its unsatisfiability must generate at least (1 + e) n clauses.", "Abstract The distribution of hard graph coloring problems as a function of graph connectivity is shown to have two distinct transition behaviors. The first, previously recognized, is a peak in the median search cost near the connectivity at which half the graphs have solutions. This region contains a high proportion of relatively hard problem instances. However, the hardest instances are in fact concentrated at a second, lower, transition point. Near this point, most problems are quite easy, but there are also a few very hard cases. This region of exceptionally hard problems corresponds to the transition between polynomial and exponential scaling of the average search cost, whose location we also estimate theoretically. These behaviors also appear to arise in other constraint problems. This work also shows the limitations of simple measures of the cost distribution, such as mean or median, for identifying outlying cases.", "" ] }

{ "cite_N": [ "@cite_20" ], "mid": [ "2107726111" ], "abstract": [ "This paper surveys the field of reinforcement learning from a computer-science perspective. It is written to be accessible to researchers familiar with machine learning. Both the historical basis of the field and a broad selection of current work are summarized. Reinforcement learning is the problem faced by an agent that learns behavior through trial-and-error interactions with a dynamic environment. The work described here has a resemblance to work in psychology, but differs considerably in the details and in the use of the word \"reinforcement.\" The paper discusses central issues of reinforcement learning, including trading off exploration and exploitation, establishing the foundations of the field via Markov decision theory, learning from delayed reinforcement, constructing empirical models to accelerate learning, making use of generalization and hierarchy, and coping with hidden state. It concludes with a survey of some implemented systems and an assessment of the practical utility of current methods for reinforcement learning." ] }

{ "cite_N": [ "@cite_19" ], "mid": [ "2137775453" ], "abstract": [ "When n identical randomly located nodes, each capable of transmitting at W bits per second and using a fixed range, form a wireless network, the throughput spl lambda (n) obtainable by each node for a randomly chosen destination is spl Theta (W spl radic (nlogn)) bits per second under a noninterference protocol. If the nodes are optimally placed in a disk of unit area, traffic patterns are optimally assigned, and each transmission's range is optimally chosen, the bit-distance product that can be transported by the network per second is spl Theta (W spl radic An) bit-meters per second. Thus even under optimal circumstances, the throughput is only spl Theta (W spl radic n) bits per second for each node for a destination nonvanishingly far away. Similar results also hold under an alternate physical model where a required signal-to-interference ratio is specified for successful receptions. Fundamentally, it is the need for every node all over the domain to share whatever portion of the channel it is utilizing with nodes in its local neighborhood that is the reason for the constriction in capacity. Splitting the channel into several subchannels does not change any of the results. Some implications may be worth considering by designers. Since the throughput furnished to each user diminishes to zero as the number of users is increased, perhaps networks connecting smaller numbers of users, or featuring connections mostly with nearby neighbors, may be more likely to be find acceptance." ] }

{ "cite_N": [ "@cite_30", "@cite_26", "@cite_22", "@cite_29", "@cite_9", "@cite_1", "@cite_32", "@cite_3", "@cite_0", "@cite_19", "@cite_2", "@cite_15", "@cite_34", "@cite_10" ], "mid": [ "2110225498", "", "2165510626", "", "2131992719", "2108190032", "", "2138203492", "2138928022", "2137775453", "59733848", "1747529848", "2105831729", "2136812100" ], "abstract": [ "We derive an information-theoretic upper bound on the rate per communication pair in a large ad hoc wireless network. We show that under minimal conditions on the attenuation due to the environment and for networks with a constant density of users, this rate tends to zero as the number of users gets large.", "", "We define and study capacity regions for wireless ad hoc networks with an arbitrary number of nodes and topology. These regions describe the set of achievable rate combinations between all source-destination pairs in the network under various transmission strategies, such as variable-rate transmission, single-hop or multihop routing, power control, and successive interference cancellation (SIC). Multihop cellular networks and networks with energy constraints are studied as special cases. With slight modifications, the developed formulation can handle node mobility and time-varying flat-fading channels. Numerical results indicate that multihop routing, the ability for concurrent transmissions, and SIC significantly increase the capacity of ad hoc and multihop cellular networks. On the other hand, gains from power control are significant only when variable-rate transmission is not used. Also, time-varying flat-fading and node mobility actually improve the capacity. Finally, multihop routing greatly improves the performance of energy-constraint networks.", "", "We consider the problem of determining rates of growth for the maximum stable throughput achievable in dense wireless networks. We formulate this problem as one of finding maximum flows on random unit-disk graphs. Equipped with the max-flow min-cut theorem as our basic analysis tool, we obtain rates of growth under three models of communication: (a) omnidirectional transmissions; (b) \"simple\" directional transmissions, in which sending nodes generate a single beam aimed at a particular receiver; and (c) \"complex\" directional transmissions, in which sending nodes generate multiple beams aimed at multiple receivers. Our main finding is that an increase of Θlog2n in maximum stable throughput is all that can be achieved by allowing arbitrarily complex signal processing (in the form of generation of directed beams) at the transmitters and receivers. We conclude therefore that neither directional antennas, nor the ability to communicate simultaneously with multiple nodes, can be expected in practice to effectively circumvent the constriction on capacity in dense networks that results from the geometric layout of nodes in space.", "We address the problem of how throughput in a wireless network scales as the number of users grows. Following the model of Gupta and Kumar, we consider n identical nodes placed in a fixed area. Pairs of transmitters and receivers wish to communicate but are subject to interference from other nodes. Throughput is measured in bit-meters per second. We provide a very elementary deterministic approach that gives achievability results in terms of three key properties of the node locations. As a special case, we obtain spl Omega ( spl radic n) throughput for a general class of network configurations in a fixed area. Results for random node locations in a fixed area can also be derived as special cases of the general result by verifying the growth rate of three parameters. For example, as a simple corollary of our result we obtain a stronger (almost sure) version of the spl radic n spl radic (logn) throughput for random node locations in a fixed area obtained by Gupta and Kumar. Results for some other interesting non-independent and identically distributed (i.i.d.) node distributions are also provided.", "", "The capacity of a particular large Gaussian relay network is determined in the limit as the number of relays tends to infinity. Upper bounds are derived from cut-set arguments, and lower bounds follow from an argument involving uncoded transmission. It is shown that in cases of interest, upper and lower bounds coincide in the limit as the number of relays tends to infinity. Hence, this paper provides a new example where a simple cut-set upper bound is achievable, and one more example where uncoded transmission achieves optimal performance. The findings are illustrated by geometric interpretations. The techniques developed in this paper are then applied to a sensor network situation. This is a network joint source-channel coding problem, and it is well known that the source-channel separation theorem does not extend to this case. The present paper extends this insight by providing an example where separating source from channel coding does not only lead to suboptimal performance-it leads to an exponential penalty in performance scaling behavior (as a function of the number of nodes). Finally, the techniques developed in this paper are extended to include certain models of ad hoc wireless networks, where a capacity scaling law can be established: When all nodes act purely as relays for a single source-destination pair, capacity grows with the logarithm of the number of nodes.", "We take a new look at the issue of network capacity. It is shown that network coding is an essential ingredient in achieving the capacity of a network. Building on recent work by (see Proc. 2001 IEEE Int. Symp. Information Theory, p.102), who examined the network capacity of multicast networks, we extend the network coding framework to arbitrary networks and robust networking. For networks which are restricted to using linear network codes, we find necessary and sufficient conditions for the feasibility of any given set of connections over a given network. We also consider the problem of network recovery for nonergodic link failures. For the multicast setup we prove that there exist coding strategies that provide maximally robust networks and that do not require adaptation of the network interior to the failure pattern in question. The results are derived for both delay-free networks and networks with delays.", "When n identical randomly located nodes, each capable of transmitting at W bits per second and using a fixed range, form a wireless network, the throughput spl lambda (n) obtainable by each node for a randomly chosen destination is spl Theta (W spl radic (nlogn)) bits per second under a noninterference protocol. If the nodes are optimally placed in a disk of unit area, traffic patterns are optimally assigned, and each transmission's range is optimally chosen, the bit-distance product that can be transported by the network per second is spl Theta (W spl radic An) bit-meters per second. Thus even under optimal circumstances, the throughput is only spl Theta (W spl radic n) bits per second for each node for a destination nonvanishingly far away. Similar results also hold under an alternate physical model where a required signal-to-interference ratio is specified for successful receptions. Fundamentally, it is the need for every node all over the domain to share whatever portion of the channel it is utilizing with nodes in its local neighborhood that is the reason for the constriction in capacity. Splitting the channel into several subchannels does not change any of the results. Some implications may be worth considering by designers. Since the throughput furnished to each user diminishes to zero as the number of users is increased, perhaps networks connecting smaller numbers of users, or featuring connections mostly with nearby neighbors, may be more likely to be find acceptance.", "", "We introduce a methodology for studying wireless ad hoc networks in a multihop traffic environment. Our approach is to use theoretical upper bounds on network performance for evaluating the effects of various design choices: we focus on power control, the queuing discipline, the choice of routing and media access protocols, and their interactions. Using this framework, we then concentrate on the problem of medium access for wireless multihop networks. We first study CSMA CA, and find that its performance strongly depends on the choice of the accompanying routing protocol. We then introduce two protocols that outperform CSMA CA, both in terms of energy efficiency and achievable throughput. The progressive back off algorithm (PBOA) performs medium access jointly with power control. The progressive rump up algorithm (PRUA) sacrifices energy efficiency in favor of higher throughput. Both protocols slot time, and are integrated with queuing disciplines that are more relaxed than the first in first out (FIFO) rule. They are totally distributed and the overhead they require does not increase with the size and node density of the network.", "We introduce a new class of problems called network information flow which is inspired by computer network applications. Consider a point-to-point communication network on which a number of information sources are to be multicast to certain sets of destinations. We assume that the information sources are mutually independent. The problem is to characterize the admissible coding rate region. This model subsumes all previously studied models along the same line. We study the problem with one information source, and we have obtained a simple characterization of the admissible coding rate region. Our result can be regarded as the max-flow min-cut theorem for network information flow. Contrary to one's intuition, our work reveals that it is in general not optimal to regard the information to be multicast as a \"fluid\" which can simply be routed or replicated. Rather, by employing coding at the nodes, which we refer to as network coding, bandwidth can in general be saved. This finding may have significant impact on future design of switching systems.", "We study communication networks of arbitrary size and topology and communicating over a general vector discrete memoryless channel (DMC). We propose an information-theoretic constructive scheme for obtaining an achievable rate region in such networks. Many well-known capacity-defining achievable rate regions can be derived as special cases of the proposed scheme. A few such examples are the physically degraded and reversely degraded relay channels, the Gaussian multiple-access channel, and the Gaussian broadcast channel. The proposed scheme also leads to inner bounds for the multicast and allcast capacities. Applying the proposed scheme to a specific wireless network of n nodes located in a region of unit area, we show that a transport capacity of spl Theta (n) bit-meters per second (bit-meters s) is feasible in a certain family of networks, as compared to the best possible transport capacity of spl Theta ( spl radic n) bit-meters s in (2000), where the receiver capabilities were limited. Even though the improvement is shown for a specific class of networks, a clear implication is that designing and employing more sophisticated multiuser coding schemes can provide sizable gains in at least some large wireless networks." ] }

{ "cite_N": [ "@cite_13" ], "mid": [ "2043144080" ], "abstract": [ "Trust management is a form of distributed access control that allows one principal to delegate some access decisions to other principals. While the use of delegation greatly enhances flexibility and scalability, it may also reduce the control that a principal has over the resources it owns. Security analysis asks whether safety, availability, and other properties can be maintained while delegating to partially trusted principals. We show that in contrast to the undecidability of classical Harrison--Ruzzo--Ullman safety properties, our primary security properties are decidable. In particular, most security properties we study are decidable in polynomial time. The computational complexity of containment analysis, the most complicated security property we study, varies according to the expressive power of the trust management language." ] }

{ "cite_N": [ "@cite_16", "@cite_13", "@cite_3" ], "mid": [ "1971903460", "", "2110936068" ], "abstract": [ "We present nesC, a programming language for networked embedded systems that represent a new design space for application developers. An example of a networked embedded system is a sensor network, which consists of (potentially) thousands of tiny, low-power \"motes,\" each of which execute concurrent, reactive programs that must operate with severe memory and power constraints.nesC's contribution is to support the special needs of this domain by exposing a programming model that incorporates event-driven execution, a flexible concurrency model, and component-oriented application design. Restrictions on the programming model allow the nesC compiler to perform whole-program analyses, including data-race detection (which improves reliability) and aggressive function inlining (which reduces resource consumption).nesC has been used to implement TinyOS, a small operating system for sensor networks, as well as several significant sensor applications. nesC and TinyOS have been adopted by a large number of sensor network research groups, and our experience and evaluation of the language shows that it is effective at supporting the complex, concurrent programming style demanded by this new class of deeply networked systems.", "", "Developing sensor network applications demands a new set of tools to aid programmers. A number of simulation environments have been developed that provide varying degrees of scalability, realism, and detail for understanding the behavior of sensor networks. To date, however, none of these tools have addressed one of the most important aspects of sensor application design: that of power consumption. While simple approximations of overall power usage can be derived from estimates of node duty cycle and communication rates, these techniques often fail to capture the detailed, low-level energy requirements of the CPU, radio, sensors, and other peripherals. In this paper, we present, a scalable simulation environment for wireless sensor networks that provides an accurate, per-node estimate of power consumption. PowerTOSSIM is an extension to TOSSIM, an event-driven simulation environment for TinyOS applications. In PowerTOSSIM, TinyOS components corresponding to specific hardware peripherals (such as the radio, EEPROM, LEDs, and so forth) are instrumented to obtain a trace of each device's activity during the simulation runPowerTOSSIM employs a novel code-transformation technique to estimate the number of CPU cycles executed by each node, eliminating the need for expensive instruction-level simulation of sensor nodes. PowerTOSSIM includes a detailed model of hardware energy consumption based on the Mica2 sensor node platform. Through instrumentation of actual sensor nodes, we demonstrate that PowerTOSSIM provides accurate estimation of power consumption for a range of applications and scales to support very large simulations." ] }

{ "cite_N": [ "@cite_3" ], "mid": [ "1582451030" ], "abstract": [ "We apply linear relation analysis [CH78, HPR97] to the verification of declarative synchronous programs [Hal98]. In this approach, state partitioning plays an important role: on one hand the precision of the results highly depends on the fineness of the partitioning; on the other hand, a too much detailed partitioning may result in an exponential explosion of the analysis. In this paper, we propose to dynamically select a suitable partitioning according to the property to be proved." ] }

{ "cite_N": [ "@cite_12" ], "mid": [ "2061901927" ], "abstract": [ "Part I. Introduction: Networks, Relations, and Structure: 1. Relations and networks in the social and behavioral sciences 2. Social network data: collection and application Part II. Mathematical Representations of Social Networks: 3. Notation 4. Graphs and matrixes Part III. Structural and Locational Properties: 5. Centrality, prestige, and related actor and group measures 6. Structural balance, clusterability, and transitivity 7. Cohesive subgroups 8. Affiliations, co-memberships, and overlapping subgroups Part IV. Roles and Positions: 9. Structural equivalence 10. Blockmodels 11. Relational algebras 12. Network positions and roles Part V. Dyadic and Triadic Methods: 13. Dyads 14. Triads Part VI. Statistical Dyadic Interaction Models: 15. Statistical analysis of single relational networks 16. Stochastic blockmodels and goodness-of-fit indices Part VII. Epilogue: 17. Future directions." ] }

{ "cite_N": [ "@cite_14", "@cite_4", "@cite_33", "@cite_9", "@cite_3", "@cite_6", "@cite_19", "@cite_27", "@cite_23", "@cite_5", "@cite_17" ], "mid": [ "1974087593", "2060460295", "", "2068557399", "1671906456", "2155969378", "2025572017", "2127775997", "", "", "" ], "abstract": [ "This paper presents the analysis and modelling of two data sets associated with the literature of hypertext as represented by the ACM Hypertext conference series. This work explores new ways of organising and accessing the vast amount of interrelated information. The first data set, including all the full papers published in this series (1987 1998), is structured and visualised as a semantic space. This semantic space provides an access point for each paper in this collection. The second data set, containing author co-citation counts based on nine conferences in the series (1989 1998), is analysed and mapped in its entirety and in three evenly distributed sub-periods. Specialties  major research fronts in the field of hypertext  are identified based on the results of a factor analysis and corresponding author co-citation maps. The names of authors in these maps are linked to the bibliographical and citation summaries of these authors on the WWW.", "This article reports findings from a study of the geographic distribution of foreign authors in the Journal of American Society for Information Science & Technology (JASIST) and Journal of Documentation (JDoc). Bibliographic data about foreign authors and their geographic locations from a 50-year publication period (1950-1999) are analyzed per 5-year period for both JASIST and JDoc. The distribution of foreign authors by geographic locations was analyzed for the overall trends in JASIST and JDoc. UK and Canadian authors are the most frequent foreign authors in JASIST. Authors from the United States and Canada are the most frequent foreign authors in JDoc. The top 10 geographic locations with highest number of foreign authors and the top 10 most productive foreign authors were also identified and compared for their characteristics and trends.", "", "As part of the celebration of twenty-five years of ACM SIGIR conferences we performed a content analysis of all papers published in the proceedings of SIGIR conferences, including those from 2002. From this we determined, using information retrieval approaches of course, which topics had come and gone over the last two and a half decades, and which topics are currently \"hot\". We also performed a co-authorship analysis among authors of the 853 SIGIR conference papers to determine which author is the most \"central\" in terms of a co-authorship graph and is our equivalent of Paul Erdos in Mathematics. In the first section we report on the content analysis, leading to our prediction as to the most topical paper likely to appear at SIGIR2003. In the second section we present details of our co-authorship analysis, revealing who is the \"Christopher Lee\" of SIGIR, and in the final section we give pointers to where readers who are SIGIR conference paper authors may find details of where they fit into the coauthorship graph.", "Using data from computer databases of scientific papers in physics, biomedical research, and computer science, we have constructed networks of collaboration between scientists in each of these disciplines. In these networks two scientists are considered connected if they have coauthored one or more papers together. We have studied many statistical properties of our networks, including numbers of papers written by authors, numbers of authors per paper, numbers of collaborators that scientists have, typical distance through the network from one scientist to another, and a variety of measures of connectedness within a network, such as closeness and betweenness. We further argue that simple networks such as these cannot capture the variation in the strength of collaborative ties and propose a measure of this strength based on the number of papers coauthored by pairs of scientists, and the number of other scientists with whom they worked on those papers. Using a selection of our results, we suggest a variety of possible ways to answer the question, \"Who is the best connected scientist?\"", "We analyze growing networks ranging from collaboration graphs of scientists to the network of similarities defined among the various transcriptional profiles of living cells. For the explicit demonstration of the scale-free nature and hierarchical organization of these graphs, a deterministic construction is also used. We demonstrate the use of determining the eigenvalue spectra of sparse random graph models for the categorization of small measured networks.", "", "Social network analysis (SNA) is not a formal theory in sociology but rather a strategy for investigating social structures. As it is an idea that can be applied in many fields, we study, in partic...", "", "", "" ] }

{ "cite_N": [ "@cite_11" ], "mid": [ "2141863299" ], "abstract": [ "The different semantics that can be assigned to a logic program correspond to different assumptions made concerning the atoms that are rule heads and whose logical values cannot be inferred from the rules. For example, the well founded semantics corresponds to the assumption that every such atom is false, while the Kripke-Kleene semantics corresponds to the assumption that every such atom is unknown. In this paper, we propose to unify and extend this assumption-based approach by introducing parameterized semantics for logic programs. The parameter holds the value that one assumes for all rule heads whose logical values cannot be inferred from the rules. We work within multi-valued logic with bilattice structure, and we consider the class of logic programs defined by Fitting.Following Fitting's approach, we define an operator that allows us to compute the parameterized semantic, and to compare and combine semantics obtained for different values of the parameter. We show that our approach captures and extends the usual semantics of conventional logic programs thereby unifying their computation." ] }

{ "cite_N": [ "@cite_21", "@cite_25" ], "mid": [ "1526328753", "1982800675" ], "abstract": [ "In order to deal with uncertainty intelligently, we need to be able to represent it and reason about it. In this book, Joseph Halpern examines formal ways of representing uncertainty and considers various logics for reasoning about it. While the ideas presented are formalized in terms of definitions and theorems, the emphasis is on the philosophy of representing and reasoning about uncertainty. Halpern surveys possible formal systems for representing uncertainty, including probability measures, possibility measures, and plausibility measures; considers the updating of beliefs based on changing information and the relation to Bayes' theorem; and discusses qualitative, quantitative, and plausibilistic Bayesian networks. This second edition has been updated to reflect Halpern's recent research. New material includes a consideration of weighted probability measures and how they can be used in decision making; analyses of the Doomsday argument and the Sleeping Beauty problem; modeling games with imperfect recall using the runs-and-systems approach; a discussion of complexity-theoretic considerations; the application of first-order conditional logic to security. Reasoning about Uncertainty is accessible and relevant to researchers and students in many fields, including computer science, artificial intelligence, economics (particularly game theory), mathematics, philosophy, and statistics.", "In this paper we give a probabilistic analog PPDL of Propositional Dynamic Logic. We prove a small model property and give a polynomial space decision procedure for formulas involving well-structured programs. We also give a deductive calculus and illustrate its use by calculating the expected running time of a simple random walk program." ] }

{ "cite_N": [ "@cite_19", "@cite_13", "@cite_23" ], "mid": [ "1712909018", "", "2109187338" ], "abstract": [ "Similarity based retrieval is of major importance for querying sequence databases. We consider formalisms based on automata, temporal logics and regular expressions for querying such databases. We define two different types of similarity measures--syntax based and semantics based. These measures are divided into a spectrum of measures based on the vector distance function that is employed. We consider norm vector distance functions and give efficient query processing algorithms when these measures are employed.", "", "Temporal logic is two-valued: formulas are interpreted as either true or false. When applied to the analysis of stochastic systems, or systems with imprecise formal models, temporal logic is therefore fragile: even small changes in the model can lead to opposite truth values for a specification. We present a generalization of the branching-time logic CTL which achieves robustness with respect to model perturbations by giving a quantitative interpretation to predicates and logical operators, and by discounting the importance of events according to how late they occur. In every state, the value of a formula is a real number in the interval [0,1], where 1 corresponds to truth and 0 to falsehood. The boolean operators and and or are replaced by min and max, the path quantifiers ∃ and ¬ determine sup and inf over all paths from a given state, and the temporal operators ♦ and □ specify sup and inf over a given path; a new operator averages all values along a path. Furthermore, all path operators are discounted by a parameter that can be chosen to give more weight to states that are closer to the beginning of the path.We interpret the resulting logic DCTL over transition systems, Markov chains, and Markov decision processes. We present two semantics for DCTL: a path semantics, inspired by the standard interpretation of state and path formulas in CTL, and a fixpoint semantics, inspired by the µ-calculus evaluation of CTL formulas. We show that, while these semantics coincide for CTL, they differ for DCTL, and we provide model-checking algorithms for both semantics." ] }

{ "cite_N": [ "@cite_23", "@cite_20" ], "mid": [ "1693225151", "2107648668" ], "abstract": [ "Despite great effort spent measuring topological features of large networks like the Internet, it was recently argued that sampling based on taking paths through the network (e.g., traceroutes) introduces a fundamental bias in the observed degree distribution. We examine this bias analytically and experimentally. For classic random graphs with mean degree c, we show analytically that traceroute sampling gives an observed degree distribution P(k) 1 k for k < c, even though the underlying degree distribution is Poisson. For graphs whose degree distributions have power-law tails P(k) k^-alpha, the accuracy of traceroute sampling is highly sensitive to the population of low-degree vertices. In particular, when the graph has a large excess (i.e., many more edges than vertices), traceroute sampling can significantly misestimate alpha.", "Considerable attention has been focused on the properties of graphs derived from Internet measurements. Router-level topologies collected via traceroute-like methods have led some to conclude that the router graph of the Internet is well modeled as a power-law random graph. In such a graph, the degree distribution of nodes follows a distribution with a power-law tail. We argue that the evidence to date for this conclusion is at best insufficient We show that when graphs are sampled using traceroute-like methods, the resulting degree distribution can differ sharply from that of the underlying graph. For example, given a sparse Erdos-Renyi random graph, the subgraph formed by a collection of shortest paths from a small set of random sources to a larger set of random destinations can exhibit a degree distribution remarkably like a power-law. We explore the reasons for how this effect arises, and show that in such a setting, edges are sampled in a highly biased manner. This insight allows us to formulate tests for determining when sampling bias is present. When we apply these tests to a number of well-known datasets, we find strong evidence for sampling bias." ] }

{ "cite_N": [ "@cite_27", "@cite_10" ], "mid": [ "1479935453", "2964134979" ], "abstract": [ "Internet maps are generally constructed using the traceroute tool from a few sources to many destinations. It appeared recently that this exploration process gives a partial and biased view of the real topology, which leads to the idea of increasing the number of sources to improve the quality of the maps. In this paper, we present a set of experiments we have conduced to evaluate the relevance of this approach. It appears that the statistical properties of the underlying network have a strong influence on the quality of the obtained maps, which can be improved using massively distributed explorations. Conversely, we show that the exploration process induces some properties on the maps. We validate our analysis using real-world data and experiments and we discuss its implications.", "The increased availability of data on real networks has favoured an explosion of activity in the elaboration of models able to reproduce both qualitatively and quantitatively the measured properties. What has been less explored is the reliability of the data, and whether the measurement technique biases them. Here we show that tree-like explorations (similar in principle to traceroute) can indeed change the measured exponents of a scale-free network." ] }

{ "cite_N": [ "@cite_17" ], "mid": [ "2047940964" ], "abstract": [ "The discovery and analysis of community structure in networks is a topic of considerable recent interest within the physics community, but most methods proposed so far are unsuitable for very large networks because of their computational cost. Here we present a hierarchical agglomeration algorithm for detecting community structure which is faster than many competing algorithms: its running time on a network with n vertices and m edges is O(m d log n) where d is the depth of the dendrogram describing the community structure. Many real-world networks are sparse and hierarchical, with m n and d log n, in which case our algorithm runs in essentially linear time, O(n log^2 n). As an example of the application of this algorithm we use it to analyze a network of items for sale on the web-site of a large online retailer, items in the network being linked if they are frequently purchased by the same buyer. The network has more than 400,000 vertices and 2 million edges. We show that our algorithm can extract meaningful communities from this network, revealing large-scale patterns present in the purchasing habits of customers." ] }

{ "cite_N": [ "@cite_15" ], "mid": [ "1548650523" ], "abstract": [ "Many problems can be expressed in terms of a numeric constraint satisfaction problem over finite or continuous domains (numeric CSP). The purpose of this paper is to show that the consistency techniques that have been developed for CSPs can be adapted to numeric CSPs. Since the numeric domains are ordered the underlying idea is to handle domains only by their bounds. The semantics that have been elaborated, plus the complexity analysis and good experimental results, confirm that these techniques can be used in real applications." ] }

{ "cite_N": [ "@cite_9" ], "mid": [ "1594857028" ], "abstract": [ "We develop a framework for addressing correctness and timeliness-of-propagation issues for reactive constraints - global constraints or user-defined constraints that are implemented through constraint propagation. The notion of propagation completeness is introduced to capture timeliness of constraint propagation. A generalized form of arc-consistency is formulated which unifies many local consistency conditions in the literature. We show that propagation complete implementations of reactive constraints achieve this arc-consistency when propagation quiesces. Finally, we use the framework to state and prove an impossibility result: that CHR cannot implement a common relation with a desirable degree of timely constraint propagation." ] }

{ "cite_N": [ "@cite_13", "@cite_12" ], "mid": [ "2085716817", "1500096329" ], "abstract": [ "Local consistency techniques have been introduced in logic programming in order to extend the application domain of logic programming languages. The existing languages based on these techniques consider arithmetic constraints applied to variables ranging over finite integer domains. This makes difficult a natural and concise modelling as well as an efficient solving of a class of N P-complete combinatorial search problems dealing with sets. To overcome these problems, we propose a solution which consists in extending the notion of integer domains to that of set domains (sets of sets). We specify a set domain by an interval whose lower and upper bounds are known sets, ordered by set inclusion. We define the formal and practical framework of a new constraint logic programming language over set domains, called Conjunto. Conjunto comprises the usual set operation symbols( n), and the set inclusion relation (). Set expressions built using the operation symbols are interpreted as relations (s s 1 = s 2 ,...). In addition, Conjunto provides us with a set of constraints called graduated constraints (e.g. the set cardinality) which map sets onto arithmetic terms. This allows us to handle optimization problems by applying a cost function to the quantiiable, i.e., arithmetic, terms which are associated to set terms. The constraint solving in Conjunto is based on local consistency techniques using interval reasoning which are extended to handle set constraints. The main contribution of this paper concerns the formal deenition of the language and its design and implementation as a practical language.", "We study from a formal perspective the consistency and propagation of constraints involving multiset variables. That is, variables whose values are multisets. These help us model problems more naturally and can, for example, prevent introducing unnecessary symmetry into a model. We identify a number of different representations for multiset variables and compare them. We then propose a definition of local consistency for constraints involving multiset, set and integer variables. This definition is a generalization of the notion of bounds consistency for integer variables. We show how this local consistency property can be enforced by means of some simple inference rules which tighten bounds on the variables. We also study a number of global constraints on set and multiset variables. Surprisingly, unlike finite domain variables, the decomposition of global constraints over set or multiset variables often does not hinder constraint propagation." ] }

{ "cite_N": [ "@cite_9", "@cite_1", "@cite_22", "@cite_23" ], "mid": [ "2096979400", "2042416159", "2155945137", "2080716125" ], "abstract": [ "Delaying-based tabling mechanisms, such as the one adopted in XSB, are non-linear in the sense that the computation state of delayed calls has to be preserved. In this paper, we present the implementation of a linear tabling mechanism. The key idea is to let a call execute from the backtracking point of a former variant call if such a call exists. The linear tabling mechanism has the following advantages over non-linear ones: (1) it is relatively easy to implement; (2) it imposes no overhead on standard Prolog programs; and (3) the cut operator works as for standard Prolog programs and thus it is possible to use the cut operator to express negation-as-failure and conditionals in tabled programs. The weakness of the linear mechanism is the necessity of re-computation for computing fix-points. However, we have found that re-computation can be avoided for a large portion of calls of directly-recursive tabled predicates. We have implemented the linear tabling mechanism in B-Prolog. Experimental comparison shows that B-Prolog is close in speed to XSB and outperforms XSB when re-computation can be avoided. Concerning space efficiency, B-Prolog is an order of magnitude better than XSB for some programs.", "Early resolution mechanisms proposed for tabling such as OLDT rely on suspension and resumption of subgoals to compute fixpoints. Recently, a new resolution framework called linear tabling has emerged as an alternative tabling method. The idea of linear tabling is to use iterative computation rather than suspension to compute fixpoints. Although linear tabling is simple, easy to implement, and superior in space efficiency, the current implementations are several times slower than XSB, the state-of-the-art implementation of OLDT, due to re-evaluation of looping subgoals. In this paper, we present a new linear tabling method and propose several optimization techniques for fast computation of fixpoints. The optimization techniques significantly improve the performance by avoiding redundant evaluation of subgoals, re-application of clauses, and reproduction of answers in iterative computation. Our implementation of the method in B-Prolog not only consumes an order of magnitude less stack space than XSB for some programs but also compares favorably well with XSB in speed.", "Tabled logic programming (LP) systems have been applied to elegantly and quickly solving very complex problems (e.g., model checking). However, techniquescurren tly employed for incorporating tabling in an existing LP system are quite complex and require considerable change to the LP system. We present a simple technique for incorporating tabling in existing LP systems based on dynamically reordering clauses containing variant callsat run-time. Our simple technique allows tabled evaluation to be performed with a single SLD tree and without the use of complex operations such as freezing of stacks and heap. It can be incorporated in an existing logic programming system with a small amount of effort. Our scheme also facilitates exploitation of parallelism from tabled LP systems. Results of incorporating our scheme in the commercial ALS Prolog system are reported.", "Infinite loops and redundant computations are long recognized open problems in Prolog. Two methods have been explored to resolve these problems: loop checking and tabling. Loop checking can cut infinite loops, but it cannot be both sound and complete even for function-free logic programs. Tabling seems to be an effective way to resolve infinite loops and redundant computations. However, existing tabulated resolutions, such as OLDT-resolution, SLG-resolution and Tabulated SLS-resolution, are non-linear because they rely on the solution-lookup mode in formulating tabling. The principal disadvantage of non-linear resolutions is that they cannot be implemented using a simple stack-based memory structure like that in Prolog. Moreover, some strictly sequential operators such as cuts may not be handled as easily as in Prolog. In this paper, we propose a hybrid method to resolve infinite loops and redundant computations. We combine the ideas of loop checking and tabling to establish a linear tabulated resolution called TP-resolution. TP-resolution has two distinctive features: (1) it makes linear tabulated derivations in the same way as Prolog except that infinite loops are broken and redundant computations are reduced. It handles cuts as effectively as Prolog; and (2) it is sound and complete for positive logic programs with the bounded-term-size property. The underlying algorithm can be implemented by an extension to any existing Prolog abstract machines such as WAM or ATOAM." ] }

{ "cite_N": [ "@cite_15", "@cite_13", "@cite_8" ], "mid": [ "", "2038225707", "1999032440" ], "abstract": [ "", "We define a natural variant of NP, MAX NP, and also a subclass called MAX SNP. These are classes of optimization problems, and in fact contain several natural, well-studied ones. We show that problems in these classes can be approximated with some bounded error. Furthermore, we show that a number of common optimization problems are complete for MAX SNP under a kind of careful transformation (called L-reduction) that preserves approximability. It follows that such a complete problem has a polynomial-time approximation scheme iff the whole class does. These results may help explain the lack of progress on the approximability of a host of optimization problems.", "We prove optimal, up to an arbitrary e > 0, inapproximability results for Max-E k-Sat for k ≥ 3, maximizing the number of satisfied linear equations in an over-determined system of linear equations modulo a prime p and Set Splitting. As a consequence of these results we get improved lower bounds for the efficient approximability of many optimization problems studied previously. In particular, for Max-E2-Sat, Max-Cut, Max-di-Cut, and Vertex cover." ] }

{ "cite_N": [ "@cite_18", "@cite_21", "@cite_2" ], "mid": [ "", "1571873445", "2068190866" ], "abstract": [ "", "Preface 1. Introduction 2. Complexity Classes 3. Boolean Constraint Satisfaction Problems 4. Characterizations of Constraint Functions 5. Implementation of Functions and Reductions 6. Classification Theorems for Decision, Counting and Quantified Problems 7. Classification Theorems for Optimization Problems 8. Input-Restricted Constrained Satisfaction Problems 9. The Complexity of the Meta-Problems 10. Concluding Remarks Bibliography Index.", "We study optimization problems that may be expressed as \"Boolean constraint satisfaction problems.\" An instance of a Boolean constraint satisfaction problem is given by m constraints applied to n Boolean variables. Different computational problems arise from constraint satisfaction problems depending on the nature of the \"underlying\" constraints as well as on the goal of the optimization task. Here we consider four possible goals: Max CSP (Min CSP) is the class of problems where the goal is to find an assignment maximizing the number of satisfied constraints (minimizing the number of unsatisfied constraints). Max Ones (Min Ones) is the class of optimization problems where the goal is to find an assignment satisfying all constraints with maximum (minimum) number of variables set to 1. Each class consists of infinitely many problems and a problem within a class is specified by a finite collection of finite Boolean functions that describe the possible constraints that may be used. Tight bounds on the approximability of every problem in Max CSP were obtained by Creignou [ J. Comput. System Sci., 51 (1995), pp. 511--522]. In this work we determine tight bounds on the \"approximability\" (i.e., the ratio to within which each problem may be approximated in polynomial time) of every problem in Max Ones, Min CSP, and Min Ones. Combined with the result of Creignou, this completely classifies all optimization problems derived from Boolean constraint satisfaction. Our results capture a diverse collection of optimization problems such as MAX 3-SAT, Max Cut, Max Clique, Min Cut, Nearest Codeword, etc. Our results unify recent results on the (in-)approximability of these optimization problems and yield a compact presentation of most known results. Moreover, these results provide a formal basis to many statements on the behavior of natural optimization problems that have so far been observed only empirically." ] }

{ "cite_N": [ "@cite_18", "@cite_26", "@cite_8", "@cite_21", "@cite_1", "@cite_3", "@cite_0", "@cite_2", "@cite_5", "@cite_10" ], "mid": [ "", "1967935161", "1999032440", "1571873445", "", "2028733517", "2097646889", "2068190866", "2084350425", "1546177704" ], "abstract": [ "", "", "We prove optimal, up to an arbitrary e > 0, inapproximability results for Max-E k-Sat for k ≥ 3, maximizing the number of satisfied linear equations in an over-determined system of linear equations modulo a prime p and Set Splitting. As a consequence of these results we get improved lower bounds for the efficient approximability of many optimization problems studied previously. In particular, for Max-E2-Sat, Max-Cut, Max-di-Cut, and Vertex cover.", "Preface 1. Introduction 2. Complexity Classes 3. Boolean Constraint Satisfaction Problems 4. Characterizations of Constraint Functions 5. Implementation of Functions and Reductions 6. Classification Theorems for Decision, Counting and Quantified Problems 7. Classification Theorems for Optimization Problems 8. Input-Restricted Constrained Satisfaction Problems 9. The Complexity of the Meta-Problems 10. Concluding Remarks Bibliography Index.", "", "A boolean constraint satisfaction problem consists of some finite set of constraints (i.e., functions from 0 1-vectors to 0, 1 ) and an instance of such a problem is a set of constraints applied to specified subsets of n boolean variables. The goal is to find an assignment to the variables which satisfy all constraint applications. The computational complexity of optimization problems in connection with such problems has been studied extensively but the results have relied on the assumption that the weights are non-negative. The goal of this article is to study variants of these optimization problems where arbitrary weights are allowed. For the four problems that we consider, we give necessary and sufficient conditions for when the problems can be solved in polynomial time. In addition, we show that the problems are NP-equivalent in all other cases. (C) 2000 Elsevier Science B.V. All rights reserved.", "By the breakthrough work of Hastad [J ACM 48(4) (2001), 798–859], several constraint satisfaction problems are now known to have the following approximation resistance property: Satisfying more clauses than what picking a random assignment would achieve is NP-hard. This is the case for example for Max E3-Sat, Max E3-Lin, and Max E4-Set Splitting. A notable exception to this extreme hardness is constraint satisfaction over two variables (2-CSP); as a corollary of the celebrated Goemans-Williamson algorithm [J ACM 42(6) (1995), 1115–1145], we know that every Boolean 2-CSP has a nontrivial approximation algorithm whose performance ratio is better than that obtained by picking a random assignment to the variables. An intriguing question then is whether this is also the case for 2-CSPs over larger, non-Boolean domains. This question is still open, and is equivalent to whether the generalization of Max 2-SAT to domains of size d, can be approximated to a factor better than (1 − 1 d2). In an attempt to make progress towards this question, in this paper we prove, first, that a slight restriction of this problem, namely, a generalization of linear inequations with two variables per constraint, is not approximation resistant, and, second, that the Not-All-Equal Sat problem over domain size d with three variables per constraint, is approximation resistant, for every d ≥ 3. In the Boolean case, Not-All-Equal Sat with three variables per constraint is equivalent to Max 2-SAT and thus has a nontrivial approximation algorithm; for larger domain sizes, Max 2-SAT can be reduced to Not-All-Equal Sat with three variables per constraint. Our approximation algorithm implies that a wide class of 2-CSPs called regular 2-CSPs can all be approximated beyond their random assignment threshold. © 2004 Wiley Periodicals, Inc. Random Struct. Alg. 2004", "We study optimization problems that may be expressed as \"Boolean constraint satisfaction problems.\" An instance of a Boolean constraint satisfaction problem is given by m constraints applied to n Boolean variables. Different computational problems arise from constraint satisfaction problems depending on the nature of the \"underlying\" constraints as well as on the goal of the optimization task. Here we consider four possible goals: Max CSP (Min CSP) is the class of problems where the goal is to find an assignment maximizing the number of satisfied constraints (minimizing the number of unsatisfied constraints). Max Ones (Min Ones) is the class of optimization problems where the goal is to find an assignment satisfying all constraints with maximum (minimum) number of variables set to 1. Each class consists of infinitely many problems and a problem within a class is specified by a finite collection of finite Boolean functions that describe the possible constraints that may be used. Tight bounds on the approximability of every problem in Max CSP were obtained by Creignou [ J. Comput. System Sci., 51 (1995), pp. 511--522]. In this work we determine tight bounds on the \"approximability\" (i.e., the ratio to within which each problem may be approximated in polynomial time) of every problem in Max Ones, Min CSP, and Min Ones. Combined with the result of Creignou, this completely classifies all optimization problems derived from Boolean constraint satisfaction. Our results capture a diverse collection of optimization problems such as MAX 3-SAT, Max Cut, Max Clique, Min Cut, Nearest Codeword, etc. Our results unify recent results on the (in-)approximability of these optimization problems and yield a compact presentation of most known results. Moreover, these results provide a formal basis to many statements on the behavior of natural optimization problems that have so far been observed only empirically.", "We consider the problem MAX CSP over multi-valued domains with variables ranging over sets of size si ≤ s and constraints involving kj ≤ k variables. We study two algorithms with approximation ratios A and B. respectively, so we obtain a solution with approximation ratio max (A, B).The first algorithm is based on the linear programming algorithm of Serna, Trevisan, and Xhafa [Proc. 15th Annual Symp. on Theoret. Aspects of Comput. Sci., 1998, pp. 488-498] and gives ratio A which is bounded below by s1-k. For k = 2, our bound in terms of the individual set sizes is the minimum over all constraints involving two variables of (1 2√s1+ 1 2√s2)2, where s1 and s2 are the set sizes for the two variables.We then give a simple combinatorial algorithm which has approximation ratio B, with B > A e. The bound is greater than s1-k e in general, and greater than s1-k(1 - (s - 1) 2(k - 1)) for s ≤ k - 1, thus close to the s1-k linear programming bound for large k. For k = 2, the bound is 4 9 if s = 2, 1 2(s - 1) if s ≥ 3, and in general greater than the minimum of 1 4S1 + 1 4s2 over constraints with set sizes s1 and s2, thus within a factor of two of the linear programming bound.For the case of k = 2 and s = 2 we prove an integrality gap of 4 9 (1 + O(n-1 2)). This shows that our analysis is tight for any method that uses the linear programming upper bound.", "We present parallel approximation algorithms for maximization problems expressible by integer linear programs of a restricted syntactic form introduced by [BKT96]. One of our motivations was to show whether the approximation results in the framework of holds in the parallel setting. Our results are a confirmation of this, and thus we have a new common framework for both computational settings. Also, we prove almost tight non-approximability results, thus solving a main open question of We obtain the results through the constraint satisfaction problem over multi-valued domains, for which we show non-approximability results and develop parallel approximation algorithms. Our parallel approximation algorithms are based on linear programming and random rounding; they are better than previously known sequential algorithms. The non-approximability results are based on new recent progress in the fields of Probabilistically Checkable Proofs and Multi-Prover One-Round Proof Systems [Raz95, Has97, AS97, RS97]." ] }

{ "cite_N": [ "@cite_18", "@cite_21", "@cite_2" ], "mid": [ "", "1571873445", "2068190866" ], "abstract": [ "", "Preface 1. Introduction 2. Complexity Classes 3. Boolean Constraint Satisfaction Problems 4. Characterizations of Constraint Functions 5. Implementation of Functions and Reductions 6. Classification Theorems for Decision, Counting and Quantified Problems 7. Classification Theorems for Optimization Problems 8. Input-Restricted Constrained Satisfaction Problems 9. The Complexity of the Meta-Problems 10. Concluding Remarks Bibliography Index.", "We study optimization problems that may be expressed as \"Boolean constraint satisfaction problems.\" An instance of a Boolean constraint satisfaction problem is given by m constraints applied to n Boolean variables. Different computational problems arise from constraint satisfaction problems depending on the nature of the \"underlying\" constraints as well as on the goal of the optimization task. Here we consider four possible goals: Max CSP (Min CSP) is the class of problems where the goal is to find an assignment maximizing the number of satisfied constraints (minimizing the number of unsatisfied constraints). Max Ones (Min Ones) is the class of optimization problems where the goal is to find an assignment satisfying all constraints with maximum (minimum) number of variables set to 1. Each class consists of infinitely many problems and a problem within a class is specified by a finite collection of finite Boolean functions that describe the possible constraints that may be used. Tight bounds on the approximability of every problem in Max CSP were obtained by Creignou [ J. Comput. System Sci., 51 (1995), pp. 511--522]. In this work we determine tight bounds on the \"approximability\" (i.e., the ratio to within which each problem may be approximated in polynomial time) of every problem in Max Ones, Min CSP, and Min Ones. Combined with the result of Creignou, this completely classifies all optimization problems derived from Boolean constraint satisfaction. Our results capture a diverse collection of optimization problems such as MAX 3-SAT, Max Cut, Max Clique, Min Cut, Nearest Codeword, etc. Our results unify recent results on the (in-)approximability of these optimization problems and yield a compact presentation of most known results. Moreover, these results provide a formal basis to many statements on the behavior of natural optimization problems that have so far been observed only empirically." ] }

{ "cite_N": [ "@cite_18", "@cite_7", "@cite_8", "@cite_6", "@cite_0", "@cite_2", "@cite_5", "@cite_13", "@cite_17" ], "mid": [ "", "1991354622", "", "2078142047", "2110423379", "2105237010", "2104130981", "", "" ], "abstract": [ "", "We develop principles and rules for achieving secrecy properties in security protocols. Our approach is based on traditional classification techniques, and extends those techniques to handle concurrent processes that use shared-key cryptography. The rules have the form of typing rules for a basic concurrent language with cryptographic primitives, the spi calculus. They guarantee that, if a protocol typechecks, then it does not leak its secret inputs.", "", "In this paper we present a formal language for specifying and reasoning about cryptographic protocol requirements. We give sets of requirements for key distribution protocols and for key agreement protocols in that language. We look at a key agreement protocol due to Aziz and Diffie that might meet those requirements and show how to specify it in the language of the NRL Protocol Analyzer. We also show how to map our formal requirements to the language of the NRL Protocol Analyzer and use the Analyzer to show that the protocol meets those requirements. In other words, we use the Analyzer to assess the validity of the formulae that make up the requirements in models of the protocol. Our analysis reveals an implicit assumption about implementations of the protocol and reveals subtleties in the kinds of requirements one might specify for similar protocols.", "Security properties such as confidentiality and authenticity may be considered in terms of the flow of messages within a network. To the extent that this characterisation is justified, the use of a process algebra such as Communicating Sequential Processes (CSP) seems appropriate to describe and analyse them. This paper explores ways in which security properties may be described as CSP specifications, how security mechanisms may be captured, and how particular protocols designed to provide these properties may be analysed within the CSP framework. The paper is concerned with the theoretical basis for such analysis. A sketch verification of a simple example is carried out as an illustration.", "We develop a typed process calculus for security protocols in which types convey secrecy properties. We focus on asymmetric communication primitives, especially on public-key encryption. These present special difficulties, partly because they rely on related capabilities (e.g., “public” and “private” keys) with different levels of secrecy and scopes.", "The authors specify authentication protocols as formal objects with precise syntax and semantics, and define a semantic model that characterizes protocol executions. They have identified two basic types of correctness properties, namely, correspondence and secrecy; that underlie the correctness concerns of authentication protocols. Assertions for specifying these properties, and a formal semantics for their satisfaction in the semantic model are defined. The Otway-Rees protocol is used to illustrate the semantic model and the basic correctness properties. >", "", "" ] }