基于广义超曲面树的相似性搜索算法

相似性搜索是数据挖掘的主要领域之一.它在数据库中检索出相似的数据,发现数据间的相似性.它可以应用于图像数据库、空间数据库和时间序列分析.对于欧氏空间(一种特殊的度量空间),相似性搜索算法中基于R-tree的方法,在低维时是高效的,当维数增加时,R-tre e的方法将退化为线性扫描.该现象被称为维数灾难(dimensionality curse),主要原因是存在数据重复.当数据量很大且维数很高时,距离计算和I/O操作将非常费时.提出了度量空间上新的空间分割方法和索引结构rgh-tree,利用数据库的数据对象与很少几个固定参考对象的距离信息进行数据分割和分布,产生一个各节点没有数据重复的平衡树.另外,在rgh-tree的基础上提出了相应的相似性搜索算法,该算法具有较小的I/O代价和距离计算次数,平均复杂性近似为o(n^0.58).解决了目前算法存在的一些问题.     

Adding structure to unstructured peer-to-peer networks: the use of small-world graphs

The “small-world” graph structure is pervasive and is observed to arise “without-design” or “naturally” in many practical systems such as the World Wide Web. In contrast to natural systems, overlay networks provide an opportunity to design structure. We seek the advantages of designing overlay topologies with small-world properties to support file sharing in peer-to-peer networks. We focus on two metrics of performance: (a) search protocol performance, a local gain perceived directly by peer-to-peer network users and (b) network utilization, a global property that is of interest to network service providers. We propose a class of overlay topologies and show, by simulation, that a particular topology instance of this class where every node has many close neighbors and few random neighbors (i.e., a small-world graph) exhibits very good properties. In this overlay topology, the chances of locating files are high, and the nodes where these files are found are, on average, close to the query source. This improvement in search protocol performance is achieved while decreasing the traffic load on the links in the underlying network. We propose a simple greedy algorithm to construct such overlay topologies where each node operates independently and in a decentralized manner to select its neighbors.     

An efficient parallel algorithm for geometrically characterising drawings of a class of 3-D objects

Labelling the lines of a planar line drawing of a 3-D object in a way that reflects the geometric properties of the object is a much studied problem in computer vision, considered to be an important step towards understanding the object from its 2-D drawing. Combinatorially, the labellability problem is a Constraint Satisfaction Problem and has been shown to be NP-complete even for images of polyhedral scenes. In this paper, we examine scenes that consist of a set of objects each obtained by rotating a polygon around an arbitrary axis. The objects are allowed to arbitrarily intersect or overlay. We show that for these scenes, there is a sequential lineartime labelling algorithm. Moreover, we show that the algorithm has a fast parallel version that executes inO(log³ n) time on an Exclusive-Read-Exclusive-Write Parallel Random Access Machine withO(n ³/log³ n) processors. The algorithm not only answers the decision problem of labellability, but also produces a legal labelling, if there is one. This parallel algorithm should be contrasted with the techniques of dealing with special cases of the constraint satisfaction problem. These techniques employ an effective, but inherently sequential, relaxation procedure in order to restrict the domains of the variables.This research was partially supported by the European Community ESPRIT Basic Research Program under contracts 7141 (project ALCOM II) and 6019 (project Insight II).     

基于P2P的自组织网络路由算法研究*

针对传统的P2P采用泛洪的信息传输方式,网络带宽开销耗费较大,而结构化P2P覆盖网又难以在开销和效率方面做到较好的权衡。根据网络的动态性,有效地建立起一个可分层的树型自治系统,详细描述了该系统的构建目标和体系结构,并基于P2P计算模式动态构建该模型,给出相应的路由发现和更新算法。在理论及仿真实验的基础上对该路由模型的性能进行了验证。结果表明,该网络是一种可运行于任何环境,不受限于系统规模大小、节点能力强弱、节点出入频率,可通过动态调节保证路由效率的广域分布式系统。     

圆与多边形重叠区域的判定算法

本文提出了一种实用的圆与多边形重叠区域的判定算法，它集判断与确定功能于一体。该算法将多边形的边视为有向线段，通过引入多边形顶点的入边，出边交点的概念，研究了圆与多边形重叠区域的确定问题，并给出了作出其重叠区域的定理。     

基于R＋树的地图叠加分析双重循环算法

地图叠加是非常重要的 GIS空间分析功能之一 ,为此 ,提出了一种新的基于 R 树空间索引的矢量地图叠加分析双重循环算法 ,首先采用多边形穷举求交方法计算出线段相交点 ;然后运用引入、引出交点交替配对的叠加结果弧线段生成原则 ,进一步实现了面面叠加和线面叠加的双重循环算法 ;最后引入 R 树空间索引对空间数据的高效存取机制 ,对算法进行改进 ,进一步提高了计算速度 .实践结果表明 ,该算法快速、有效 ,具有较强的应用价值 .     

Efficient algorithm for polygon overlay for dense map image data sets

A map consists of a finite set of mutually disjoint polygons. A data structure and efficient algorithm for polygon overlay of dense map image data sets are discussed. The data structure, referred to as the ending-x structure, is a variant of the y-partition structure developed by Merrill which is still widely acclaimed as an optimum raster data structure. The modest refinement of the ending-x structure further reduces raster data volume. More importantly, it can significantly enhance the process of polygon overlay for multiple map image data sets. Considering the density of many map image data sets, and the significance of the polygon overlay problem to spatial data handling, these are significant advances. The paper describes the ending-x data structure and compares the algorithm for polygon overlay suggested by Merrill with one employing the ending-x structure.     

KONHEIM'S CRYPTOGRAPHY–A PRIMER: A BOOK REVIEW

In this paper, we present an approach to compute master keys for an M ³ public-key cryptoscfaeme. At first, the existence conditions of master keys are derived. Then an algorithm to compute master keys is given. Further, the security of our master key cryptosystem is also guaranteed, no matter what relations or key values are exposed.     

一种构造自愿计算网络的新方法

虽然Peer-to-Peer结构的可扩展性已经成为普遍的共识，但如何简单、有效地构造具有良好特性的P2P计算网络仍然是一个开放问题。本文提出了一个自组织的Peer-to-Peer重叠计算网络的构造方法以及基于该网络的计算任务调度算法。仿真结果说明，本文构造的计算网络表现出明显的自组织特性，具有较好的可扩展性和自组织能力，能较好地为计算资源的调度提供支持。     

Convergence and refinement of the Wang-Landau algorithm

Recently, Wang and Landau proposed a new random walk algorithm that can be very efficiently applied to many problems. Subsequently, there has been numerous studies on the algorithm itself and many proposals for improvements were put forward. However, fundamental questions such as what determines the rate of convergence has not been answered. To understand the mechanism behind the Wang-Landau method, we did an error analysis and found that a steady state is reached where the fluctuations in the accumulated energy histogram saturate at values proportional to [log(f)]^−1/2. This value is closely related to the error corrections to the Wang-Landau method. We also study the rate of convergence using different “tuning” parameters in the algorithm.     

SemreX: Efficient search in a semantic overlay for literature retrieval

The World Wide Web is growing at such a pace that even the biggest centralized search engines are able to index only a small part of the available documents on the Internet. The decentralized structure, together with the features of self-organization and fault-tolerance, makes peer-to-peer networking an effective information-sharing model; however, content searching still remains a serious challenge of large scale peer-to-peer networks. In this paper we present SemreX, a semantic overlay for desktop literature/ document retrieval in peer-to-peer networks. We present a semantic overlay algorithm by which semantically similar peers are locally clustered together, and long-range connections are rewired for a short-cut in peer-to-peer networks. Based on the semantic overlay, a heuristic query routing algorithm is proposed for efficient content searching. We conduct a comprehensive simulation to evaluate the search performance of our algorithms. Results show that search in our SemreX semantic overlay greatly improves search efficiency.     

Dynamic Multicast in Overlay Networks with Linear Capacity Constraints

In a peer-to-peer overlay network, the phenomenon of multiple overlay links sharing bottleneck physical links leads to correlation of overlay link capacities. We are able to more accurately model the overlay by incorporating these linear capacity constraints (LCCs). We formulate the problem of maximizing bandwidth in overlay multicast using our LCC model. We show that finding a maximum bandwidth multicast tree in an overlay network with LCC is NP-complete. Therefore, an efficient heuristics algorithm is designed to solve the problem. Extensive simulations show that our algorithm is able to construct multicast trees that are optimal or extremely close to optimal, with significantly higher bandwidth than trees formed in overlays with no LCC. Furthermore, we develop a fully distributed algorithm for obtaining near-optimal multicast trees, by means of gossip-based algorithms and a restricted but inherently distributed class of LCC (node-based LCC). We demonstrate that the distributed algorithm converges quickly to the centralized optimal and is highly scalable.     

An optimal inherently stabilizing routing algorithm for star P2P overlay networks

Star graphs possess many desirable properties such as scalable node degrees and diameters, which are essential to facilitate reduced routing table sizes and low maximum path length for routing in large P2P networks. In addition, because a large number of disjoint paths are available and each data/replica in an n‐star can be placed in an (n − 1)‐star, load balancing and alleviation of network bottlenecks can be implemented in star P2P overlay networks. Therefore, star networks have been proposed as viable alternatives to existing overlay topologies for large P2P networks. In this paper, we propose an optimal stabilizing and inherently stabilizing algorithm for routing messages over all disjoint paths between two peers in a star P2P overlay network. The algorithm is optimal in terms of its time complexity in rounds and the length of the longest path traversed by the messages, and fault tolerant due to being stabilizing and inherently stabilizing, allowing the system to withstand transient faults. The algorithm can be used to increase network reliability and survivability in P2P networks. In addition, the usage of all disjoint paths to route messages between two peers leads to increased network bandwidth while distributing the communication overhead across the network and eliminating network bottlenecks in P2P networks. Copyright © 2016 John Wiley & Sons, Ltd.     

Bi-criteria and tri-criteria analysis to minimize maximum lateness makespan and resource consumption for scheduling a single machine

We analyze two single machine scheduling problems for the case where job processing times are controllable, by allocating continuous and non-renewable resources to the processing operations. The first problem to analyze is constructing the trade-off curve between maximum lateness and total resource consumption; an O(n ²) computational time optimization algorithm was constructed to solve this problem. This algorithm was extended to solve the second problem, which is to construct the trade-off surface between maximum lateness, makespan, and total resource consumption. As part of this algorithm we identify a plane in the 3D field that is formed by the three criteria, which is parallel only to the maximum lateness, and calculate the optimal makespan and total resource consumption as functions of points on this plane. The extended algorithm keeps the same complexity of O(n ²) time. Both algorithms are very robust as they solve the problem for a very large set of resource consumption functions which has to follow only some mild (and commonly acceptable) conditions. Moreover, as far as we know, this is the first research of its kind in the field of multi-objective scheduling to present an algorithm that constructs a 3D trade-off surface.     

语义对等覆盖网中社区结构的发现和评价

最近,通过建立语义覆盖网络来提高大规模分布式网络环境中信息检索服务的性能成为对等计算领域的研究热点.目前,研究者们在语义覆盖协议和搜索算法方面已经做了大量研究,证明了语义覆盖在基于对等网络模型的内容定位应用方面极为有效.然而,分析和评价语义覆盖网络特征的研究工作确非常有限.文中通过建立数学模型和设计启发式回溯-贪婪混合算法、确认了语义覆盖网络的一种主要内在特性——社区结构特性.利用评价模型比较了SemreX语义覆盖网络和Gnutella网络的性能,实验结果显示SemreX覆盖网具有显著的社区结构特征,而Gnutella网络却没有这样的特征.另外,通过分别在两种覆盖网中仿真洪泛协议发现具有显著社区结构特征的覆盖网在内容定位方面效率更高.     

一种基于局部歧义词网格的快速分词算法

提出了局部歧义词网格的概念,针对汉语分词中的覆盖歧义,提出了一种使用迭代算法训练覆盖歧义词典的算法,得到覆盖歧义候选词条词典。在此基础上提出了一种基于局部歧义词网格的、能够检测汉语分词过程中产生的组合歧义和覆盖歧义的分词算法,该算法仅考虑存在歧义的局部歧义词网格,并将对覆盖歧义的处理简化为查询覆盖歧义候选词典,因此,该算法的时间复杂度大幅下降。实验结果表明,该算法能够实现快速的汉语分词,且其分词正确率能够达到97%以上。     

主题重叠网络的构造与搜索算法研究

结构化P2P网络虽然具有扩展性良好的数据查找机制,但只支持基于键的准确匹配搜索.为提供更丰富的数据查询能力,本文提出一种基于主题重叠网络的结构化P2P搜索算法--主题重叠网络搜索算法(TONS).其基本思想是在结构化P2P网络之上,将结点按主题组织成分层的重叠网络,使含有相似主题的结点相互链接在一起;利用主题中继结点所具有的全局导航能力,TONS能够基于内容将查询限定在P2P网络的局部范围内,并且通过在重叠网络中随机添加一些长距离链接,使重叠网络具有Small-World特性,改善TONS的搜索性能.实验结果表明,TONS大大提高了搜索的查全率,减少了P2P网络信息搜索时的平均路径距离和平均消息数目.     

GrouPeer: Dynamic clustering of P2P databases

Sharing structured data in a P2P network is a challenging problem, especially in the absence of a mediated schema. The standard practice of answering a consecutively rewritten query along the propagation path often results in significant loss of information. On the opposite, the use of mediated schemas requires human interaction and global agreement, both during creation and maintenance. In this paper we present GrouPeer, an adaptive, automated approach to both issues in the context of unstructured P2P database overlays. By allowing peers to individually choose which rewritten version of a query to answer and evaluate the received answers, information-rich sources left hidden otherwise are discovered. Gradually, the overlay is restructured as semantically similar peers are clustered together. Experimental results show that our technique produces very accurate answers and builds clusters that are very close to the optimal ones by contacting a very small number of nodes in the overlay.     

Multi-channel live streaming in service overlay network

Service overlay network (SON) provides an effective means to deploy quality of service (QoS)-guaranteed live streaming over today’s Internet. A major challenge in designing such a network is dealing with resource sharing among multiple channels. To achieve the best overall QoS in SON, we devise a new multi-channel live streaming scheme. First, we propose a multi-tree construction algorithm by infrastructure-based overlay multicast. The algorithm employs pre-allocated session degree constraints in overlay nodes to reserve resources for multiple channels, and constructs multiple trees by considering the total resource utilization of overlay nodes. Second, we propose a tree-aware queue scheduling algorithm to reduce the overlay processing delay in view of the entire overlay network. Scheduling priority is identified to trade off session priority with node location in different trees. From simulation and experimental results, the scheme achieves a differentiated control among different sessions, provides load balancing among overlay nodes, and improves the delay performance on SON.     

Efficient distributed snapshots in an anonymous asynchronous message-passing system

We present a global snapshot algorithm with concurrent initiators, with termination detection in an anonymous asynchronous distributed message-passing system having FIFO channels. In anonymous systems, process identifiers are not available and an algorithm cannot use process identifiers in its operation. Such systems arise in several domains due to a variety of reasons. In the proposed snapshot algorithm for anonymous systems, each instance of algorithm initiation is identified by a random number (nonce); however, this is not used as an address in any form of communication. In the algorithm, each process can determine an instant when the local snapshot recordings at all the processes have terminated. This is a challenging problem when an algorithm cannot use process identifiers and a process does not know the number of processes in the system or the diameter of the network and cannot use a predefined topology overlay on the network, because there is no easy way to identify the global termination condition. The message complexity of our algorithm is (cn²)$\left(c{n}^2\right)$, where c$c$ is the number of concurrent initiators and n$n$ is the number of processes in the system, which is much better than that of the algorithm by Chalopin et al. (2012) [6]. Further, the algorithm by Chalopin et al. also requires knowledge of the network diameter.