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Reduced complexity tree-structured conditional random field for all-words word sense disambiguation

Journal of Computational Information Systems 2012年第3期8卷 1177-1186页

作者： Zhou, Yun Wang, Ting Wang, Zhiyuan Xie, Songxian Computer School National University of Defense Technology Changsha 410073 China National Key Laboratory for Parallel and Distributed Processing National University of Defense Technology Changsha 410073 China

In this paper, we apply tree-structured conditional random field (TCRF) to all-words word sense disambiguation (WSD), where the graphical structure of TCRF is the dependency syntax tree produced by Minipar. The extremely large label space and high time complexity of TCRF hinders its application in semantic parsing, especially in all-words WSD, and we focus on reducing the time complexity of TCRF in this paper. The running time of TCRF is reduced significantly by edge feature selection and parallelization in training phase and beam search strategy in decoding phase. We evaluate the TCRF method on the English all-words task of Senseval-3, and the F1 value of TCRF method is 0.668, which outperforms the best result 0.652 in Senseval-3. For convenience of comparison, our training set only includes a part of Semcor, which reserves the space for improvement. Furthermore, the practical problem in the fields of information retrieval and natural language processing, often has a large label space and tree-structured information, which can also be solved by the TCRF method proposed in this paper. 1553-9105/Copyright © 2012 Binary Information Press.

关键词： Semantics

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Precise pointer analysis for list-manipulating programs based on quantitative separation logic

Precise pointer analysis for list-manipulating programs base...

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International Conference on Information Science and Technology (ICIST)

作者： Longming Dong Liqian Chen Jiangchao Liu Renjian Li National Laboratory for Parallel and Distributed Processing School of Computer National University of Defense Technology Changsha China

Full precise pointer analysis has been a challenging problem, especially when dealing with dynamically-allocated memory. Separation logic can describe pointer alias formally, but cannot describe the quantitative reachability between pointers. In this paper, we present a symbolic framework for analyzing the reachability between pointers in list-manipulating programs. The precise points-to relations of pointers in lists are described by formulae of quantitative separation logic (QSL), and the analysis framework is based on the operational and rearrangement rules about the assignments of pointers. The fixpoint calculus and the counter symbolic abstraction are used to find loop invariants. We can get precise relations between pointers at each point of list-manipulating programs. In the end, several initial examples about list-manipulating programs are given to show that the approach can get precise pointer analysis for list-manipulating programs.

关键词： Radiation detectors Shape Instruments Calculus Semantics Data structures Argon

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Invalid Pointer Dereferences Detection for CPS Software Based on Extended Pointer Structures

Invalid Pointer Dereferences Detection for CPS Software Base...

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International Conference on Secure Software Integration and Reliability Improvement Companion (SSIRI-C)

作者： Longming Dong Wei Dong Liqian Chen National Laboratory for Parallel and Distributed Processing School of Computer National University of Defense Technology Changsha China

Invalid pointer dereferences, such as null pointer dereferences, dangling pointer dereferences and double frees, are a prevalent source of software bugs in CPS software, due to flexible dereferencing pointers along various pointer fields. Existing tools have high overhead or are incomplete, thereby limiting their efficiency in checking the kind of CPS software with shared and mutable memory. In this paper, we present a novel extended pointer structure for detecting all invalid pointer dereferences in this kind of CPS software. We propose an invalid pointer dereferences detection algorithm based on the uniform transformation of abstract heap states. Experimental evaluation about a set of large C benchmark programs shows that the proposed approach is sufficiently efficient in detecting invalid pointer dereferences of CPS software with shared and mutable memory.

关键词： Abstracts Software Frequency modulation Semantics Switches Detection algorithms Runtime

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Skyline Query processing on Interval Uncertain Data

Skyline Query Processing on Interval Uncertain Data

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IEEE International Symposium on Object/Component/Service-Oriented Real-Time distributed Computing Workshops (ISORCW)

作者： Xiaoyong Li Yijie Wang Xiaoling Li Guangdong Wang National Laboratory for Parallel and Distributed Processing School of Computer Science National University of Defense Technology Changsha China

Many recent applications involve processing and analyzing uncertain data. Recently, several research efforts have addressed answering skyline queries efficiently on massive uncertain datasets. However, the research lacks methods to compute these queries on uncertain data, where each dimension of the uncertain object is represented as an interval or an exact value. In this paper, we extensively study the problem of skyline query on these interval based uncertain objects, which has never been studied before. We first model the problem of querying the skylines on interval datasets. Typically, we address two efficient algorithms with I/O optimal for the conventional interval skyline queries and constrained interval skyline queries, respectively. Extensive experiments demonstrate the efficiency of all our proposed algorithms.

关键词： Probability density function Distribution functions Probability distribution Random variables Computational modeling Uncertainty distributed databases

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A study of strategies to restrain the C&C activities of structured P2P botnets

A study of strategies to restrain the C&C activities of stru...

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International Conference on Computer Sciences and Convergence Information Technology (ICCIT)

作者： Tianzuo Wang Bo Liu Huaimin Wang Hao Ren Xiaolong Ma School of Computer Science National Laboratory for Parallel and Distributed Processing National University of Defense and Technology Changsha China

Botnets are threatening the Internet heavily, and more and more botnets are utilizing the P2P technology to build their C&C (Command and Control) mechanisms. Some research have been made to compare the resilience of structured P2P botnets and unstructured ones, against elimination of nodes, but the problem that which eliminating strategy is the best is rarely studied. In this paper, we proposed a new metric called the half point, to measure the effectiveness of different strategies. We also selected seven different eliminating strategies and compared them. Through extensive simulations, we find that RBC is the best eliminating strategy. Further analysis shows that for the strategy RBC, the average degree of nodes in the botnet have the most significant influence. The bigger the average degree is, the bigger the half point of RBC is, which implies that node eliminating may not be a reasonable choice for mitigating botnets with big average degree. Results of this paper can provide guidance for restraining structured P2P botnets.

关键词： C&C mechanism betweenness centrality coreness eliminating strategy half point restrain structured P2P botnets

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SMP-SIM: An event-driven performance simulator for SMP

SMP-SIM: An event-driven performance simulator for SMP

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International Conference on Systems and Informatics (ICSAI)

作者： Xin Zhang Yuhua Tang Yufei Lin Xinhai Xu Xiaowei Guo Xiaoguang Ren National Laboratory for Parallel and Distributed Processing School of Computer National University of Defense Technology Changsha Hunan China

Performance prediction for the high performance computer system is of great importance for designing, implementing, and optimizing system. As a widely used technique for predicting performance, simulation method attracts more and more attention from the research community. Based on analyzing the problems in the current performance simulation techniques, we present a key idea of the performance simulator for SMP system based on event-driven. We propose the framework of SMP-SIM and implement it based on MPICH2. The simulation results show that, our simulation technique has the advantages of high accuracy and simulation performance.

关键词： Computational modeling Switches Clocks Educational institutions Computers Predictive models Analytical models

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Bodhi: Detecting Buffer Overflows with a Game

Bodhi: Detecting Buffer Overflows with a Game

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International Conference on Secure Software Integration and Reliability Improvement Companion (SSIRI-C)

作者： Jie Chen Xiaoguang Mao School of Computer National University of Defense Technology Changsha China National Laboratory for Parallel and Distributed Processing Changsha China

Buffer overflow is one of the most dangerous and common vulnerabilities in CPS software. Despite static and dynamic analysis, manual analysis is still heavily used which is useful but costly. Human computation harness humans' time and energy in a way of playing games to solve computational problems. In this paper we propose a human computation method to detect buffer overflows that does not ask a person whether there is a potential vulnerability, but rather a random person's idea. We implement this method as a game called Bodhi in which each player is shown a piece of code snippet and asked to choose whether their partner would think there is a buffer overflow vulnerability at a given position in the code. The purpose of the game is to make use of the rich distributed human resource to increase effectiveness of manual detection for buffer overflows. The game has been proven to be efficient and enjoyable in practice.

关键词： Games Buffer overflow Humans Software Servers Manuals Programming

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Detecting faults by tracing companion states in cloud computing systems

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Jisuanji Xuebao/Chinese Journal of Computers 2012年第5期35卷 856-870页

作者： Rao, Xiang Wang, Huai-Min Chen, Zhen-Bang Zhou, Yang-Fan Cai, Hua Zhou, Qi Sun, Ting-Tao National Key Laboratory for Parallel and Distributed Processing National University of Defense Technology Changsha 410073 China Shenzhen Research Institute The Chinese University of Hong Kong Shenzhen China Department of Computing Platform Alibaba Cloud Computing Company Hangzhou 310011 China

A common way to construct a fault model is injecting the fault into the system and observing the subsequent symptoms, e. g. event logs. However, fault features would vary during the propagation period, and present different symptoms at different stage of the fault propagation process. The exiting detection window based feature extraction methods can only identify the early symptoms of a fault, but fail to detect the latter symptoms and cause false alarms. To solve the problem, we present a fault feature extraction method, called Companion State Tracer (CSTracer), which consists of 3 integrated steps: (1) pre-process logs to remove the unrelated logs;(2) construct a general identifier for the early symptoms of a fault;(3) construct a finite state machine model for the fault to trace the latter symptoms. CSTracer can persistently monitor a fault after the fault has been identified. We have justified the effectiveness of CSTracer in an enterprise cloud system. Compared with the existing, the results show that CSTracer has a better detection accuracy.

关键词： Fault detection

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Server-uncertain spectrum trading in cognitive radio networks: A queueing-theoretic modeling approach

Server-uncertain spectrum trading in cognitive radio network...

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International Conference on Cognitive Radio Oriented Wireless Networks and Communications

作者： Lixia Liu Gang Hu Ming Xu Yuxing Peng National Key Laboratory for Parallel and Distributed Processing National University of Defense Technology Changsha China Department of Network Engineering College of Computer National University of Defense Technology Changsha China

Spectrum trading is the promising method to improve spectrum efficiency from the perspective of economics. In this paper we propose a queueing-theory based spectrum trading model, where the primary user plays the server role providing spectrum to the secondary user who acts as the customer. The most significant challenge is how to optimize the spectrum trading model considering the server uncertainty which includes service state, service time, service area, service content and service price. We design a STACP queueing model according to the server attributes, so that the secondary user can choose the right queue quickly and reasonably according to its demand. Moreover, we further analyze the optimizing strategies for STACP model which can maximize the profit of the primary user and minimize the service cost of the secondary user. The simulation results demonstrate the analysis results.

关键词： Servers Uncertainty Loss measurement Queueing analysis Economics Analytical models Business

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Some critical problems of botnets

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Jisuanji Xuebao/Chinese Journal of Computers 2012年第6期35卷 1192-1208页

作者： Wang, Tian-Zuo Wang, Huai-Min Liu, Bo Shi, Pei-Chang Institute of Network and Information Security School of Computer Science National University of Defense Technology Changsha 410073 China National Laboratory for Parallel and Distributed Processing School of Computer Science National University of Defense Technology Changsha 410073 China

As a complex, flexible and effective platform for network attacking, the botnet spreads widely in the Internet. Botnets can provide the botmasters with the ability to launch large-scale malicious activities such as spamming and DDoS (distributed Denial of Service) attacks. Botnets are continuously bringing more and more severe threats, so that the study on botnets has already become one of the focuses in the field of network security. However, in recent years, some new developments of botnets are challenging the existing understanding on botnets. In this paper, according to the new conditions of botnets and the researches in existence, a definition of botnet is proposed based on the works of other researchers, taxonomies of botnets are introduced respectively from the views of network structure, dependency and delivery pattern of C&C (Command and Control) information. Then the techniques on detecting, measuring and restraining botnets are analyzed systematically. In the end, we give the evolution trends of botnets and the future research trends in this area.

关键词： Botnet

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