TBSN:一种基于分类层次的P2P网络

构建语义覆盖网络是支持基于语义的搜索、提高P2P网络查找性能和可扩展性的重要手段.现有的基于分类层次的P2P语义覆盖网络并不能充分利用分类层次所包含的语义信息,为此提出了一种基于分类层次的P2P网络(TBSN),该网络充分考虑遵循某种分类层次的数据源的特点,能够利用分类层次所包含的语义信息,动态地将peer节点聚簇成不同的语义簇,语义簇之间根据语义关系建立相应的语义路由,从而形成了一种基于语义的P2P网络.每个语义簇由一个super-peer节点和多个peer节点组成,仅负责回答其语义子空间上的查询.查询根据语义首先被路由到可能有结果的语义簇中,然后转发给相关的peer节点,从而减少查询所涉及的节点和消息的数量,提高了网络的性能.实验表明,TBSN网络在查找性能和开销之间取得了良好的平衡,同时较好地保持了语义簇之间的负载平衡和簇中数据之间的语义关系.     

Tree-Based Index Overlay in Hybrid Peer-to-Peer Systems

Hybrid Peer-to-Peer(P2P) systems that construct overlay networks structured among superpeers have great potential in that they can give the benefits such as scalability,search speed and network traffic,taking advantages of superpeer-based and the structured P2P systems.In this article,we enhance keyword search in hybrid P2P systems by constructing a tree-based index overlay among directory nodes that maintain indices,according to the load and popularity of a keyword.The mathematical analysis shows that t...     

Enabling Dynamic Querying over Distributed Hash Tables

Dynamic querying (DQ) is a search technique used in unstructured peer-to-peer (P2P) networks to minimize the number of nodes that is necessary to visit to reach the desired number of results. In this paper, we introduce the use of the DQ technique in structured P2P networks. In particular, we present a P2P search algorithm, named DQ-DHT (Dynamic Querying over a Distributed Hash Table), to perform DQ-like searches over DHT-based overlays. The aim of DQ-DHT is twofold: allowing arbitrary queries to be performed in structured P2P networks and providing dynamic adaptation of the search according to the popularity of the resources to be located. DQ-DHT has been particularly designed for use in those distributed environments, like computational grids, where it is necessary to support arbitrary queries for searching resources on the basis of complex criteria or semantic features. This paper describes the DQ-DHT algorithm using Chord as basic overlay and analyzes its performance in comparison with DQ in unstructured networks.     

一种基于分组的语义对等网络

以语义网络理论为基础,结合GCNET拓扑结构,提出一种基于分组的语义对等网络——Semantic GCNET,充分利用GCNET网络具有小世界特征的优点,确保其搜索限制在与查询主题相关的局部节点子集中,解决其他一些语义对等网络对主题群搜索低效的问题,克服一些语义对等网络仅支持精确匹配查找的缺点。实验结果表明,Semantic GCNET具有高效的语义查询性能和查全率。     

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.     

SemreX:一种基于语义相似度的P2P覆盖网络

对等(peer-to-peer)网络的非集中结构、良好的自治性及容错性等特征,使其可能成为Internet上有效的信息共享模型.然而,内容定位问题仍然是大规模P2P网络中信息共享所面临的挑战.SemreX系统是一种P2P网络环境下的文献检索系统.针对SemreX系统,提出一种基于语义相似度的P2P拓扑管理和查询路由算法.仿真实验结果表明,语义拓扑能够有效地提高系统的搜索效率.     

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.     

SSW: A Small-World-Based Overlay for Peer-to-Peer Search

Peer-to-peer (P2P) systems have become a popular platform for sharing and exchanging voluminous information among thousands or even millions of users. The massive amount of information shared in such systems mandates efficient semantic-based search instead of key-based search. The majority of existing proposals can only support simple key-based search rather than semantic-based search. This paper presents the design of an overlay network, namely, semantic small world (SSW), that facilitates efficient semantic-based search in P2P systems. SSW achieves the efficiency based on four ideas: 1) semantic clustering, where peers with similar semantics organize into peer clusters, 2) dimension reduction, where to address the high maintenance overhead associated with capturing high-dimensional data semantics in the overlay, peer clusters are adaptively mapped to a one-dimensional naming space, 3) small world network, where peer clusters form into a one-dimensional small world network, which is search efficient with low maintenance overhead, and 4) efficient search algorithms, where peers perform efficient semantic-based search, including approximate point query and range query in the proposed overlay. Extensive experiments using both synthetic data and real data demonstrate that SSW is superior to the state of the art on various aspects, including scalability, maintenance overhead, adaptivity to distribution of data and locality of interest, resilience to peer failures, load balancing, and efficiency in support of various types of queries on data objects with high dimensions.     

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.     

Semantic partitioning of peer-to-peer search space

Peer-to-peer (P2P) networks are beginning to form the infrastructure of future applications. Computers are organized in P2P overlay networks to facilitate search queries with reasonable cost. So, scalability is a major aim in design of P2P networks. In this paper, to obtain a high factor of scalability, we partition network search space using a consistent static shared upper ontology. We name our approach semantic partition tree (SPT). All resources and queries are annotated using the upper ontology and queries are semantically routed in the overlay network. Also, each node indexes addresses of other nodes that possess contents expressible by the concept it maintains. So, our approach can be conceived as an ontology-based distributed hash table (DHT). Also, we introduce a lookup service for the network which is very scalable and independent of the network size and just depends on depth of the ontology tree. Further, we introduce a broadcast algorithm on the network. We present worst case analysis of both lookup and broadcast algorithms and measure their performance using simulation. The results show that our scheme is highly scalable and can be used in real P2P applications.     

在P2P网络中构建支持语义搜索的覆盖网络DOverlay

P2P网络上构建支持复杂语义请求的覆盖网络是一个新的挑战.支持复杂语义的覆盖网络不仅要满足P2P网络的完全分布性、动态性、可扩展性等相关特性,还要尽量提高P2P网络的可靠性和低成本维护性.提出的非结构化领域覆盖网络DOverlay由于其资源特征是直接由其对应领域本体的概念树转换而来,因此资源可自动形成相关聚类.而基于DOverlay的资源搜索策略D_Search不仅在减少了网络开销的前提下增大了搜索成功率,而且在Dl_Search中设计的资源评级策略还大大增加了搜索的有效性.     

一个P2P搜索引擎的架构和实现

P2P搜索技术是P2P研究中的一个重要的领域。本文介绍了一个基于P2P结构化覆盖网络的分布式搜索引擎的架构和实现。该搜索引擎采用了三层架构,良好的层次架构减少了搜索引擎核心算法与P2P覆盖网络协议和具体应用间的依赖,使得搜索引擎可以移植到不同的P2P结构化覆盖网络之上。由于P2P搜索过程中会消耗大量的网络带宽,所以该搜索引擎使用了一些优化算法,它们不仅减少搜索过程带来的带宽消耗,而且保证了系统的可伸缩性。     

具有小世界特性的语义覆盖网络模型

目前大多数的结构化覆盖网络模型忽略节点的聚类性和对称性,并且只能提供精确的资源查询机制。为此,给出一种具有小世界特性的语义覆盖网络模型。该模型采用显式分区机制、语义搜索链和组扩散机制。分析和实验结果表明,该模型比现有的覆盖网络模型Chord和CAN具有更好的网络性能,搜索效率更高,且具有较好的多匹配结果查询能力。     

支持语义的P2P搜索研究

传统的P2P系统基于单特征词搜索,且不支持语义,有一定的局限性。向量空间模型VSM技术的应用解决了P2P系统中多特征词搜索的问题;标识符空间的分割,使相似文档在邻近的节点范围内聚集,提高了搜索的速度;语义思想的应用,使P2P系统能够理解搜索请求,有利于检索性能,特别是查全率的提高。仿真实验的结果表明:实现了多特征词的搜索;搜索收敛的速度较快;支持语义,检索性能得到了提高;节点达到了较好的负载平衡。     

语义覆盖网最佳规模的数学分析

现在大量研究者通过语义覆盖网构建来提高P2P网络资源查询效率,但在语义覆盖网最佳规模大小上缺乏研究。考虑运用数学方法对语义覆盖网络进行数据建模,对路由算法的路由性能指标的求解方法进行研究,并分析语义覆盖网规模与路由性能指标之间的关系。通过模型的分析和求解,得出了社区的最佳规模大小,为语义覆盖网构建与研究提供了有力的支撑。     

A scalable P2P platform for the knowledge grid

The knowledge grid needs to operate with a scalable platform to provide large-scale intelligent services. A key function of such a platform is to efficiently support various complex queries in a dynamic large-scale network environment. This paper proposes a platform to support index-based path queries by incorporating a semantic overlay with an underlying structured P2P network that provides object location and management services. Various distributed indexing structures can be dynamically formed by publishing, semantic objects as indexing nodes. Queries are forwarded along the chains of semantic object pointers to search for objects. We investigate the deployment of a scalable distributed trie index for broadcast queries on key strings, propose a decentralized load balancing method for solving the problem of uneven load distribution incurred by heterogeneity of loads and node capacities and by the distributed trie index, and give an approach for improving the availability of the semantic overlay and its trie index. Experiments demonstrate the scalability of the proposed platform.     

SSON：一种基于结构化P2P网络路由的语义覆盖网络结构

本文基于结构化P2P网络路由机制,采用基于主题划分的方法,提出了基于结构化P2P网络路由的语义覆盖网络SSON。SSON通过结构化P2P网络的标识符映射机制,根据资源类别将结点组织成层次化的覆盖网络,该覆盖网络结构确保搜索限制在与查询主题相关的局部结点子集中。该结构充分利用了结构化P2P网络的优点,解决了基于非结构化P2P网络建立的语义覆盖网络的对主题群的搜索低效问题,同时克服了结构化P2P网络仅支持精确匹配查找的缺点,为结构化P2P网络提供了可靠、高效的语义查询机制,极大地提高了查全率。     

PGSW-OS: a novel approach for resource management in a semantic web operating system based on a P2P grid architecture

A web operating system is an operating system that users can access from any hardware at any location. A peer-to-peer (P2P) grid uses P2P communication for resource management and communication between nodes in a grid and manages resources locally in each cluster, and this provides a proper architecture for a web operating system. Use of semantic technology in web operating systems is an emerging field that improves the management and discovery of resources and services. In this paper, we propose PGSW-OS (P2P grid semantic Web OS), a model based on a P2P grid architecture and semantic technology to improve resource management in a web operating system through resource discovery with the aid of semantic features. Our approach integrates distributed hash tables (DHTs) and semantic overlay networks to enable semantic-based resource management by advertising resources in the DHT based upon their annotations to enable semantic-based resource matchmaking. Our model includes ontologies and virtual organizations. Our technique decreases the computational complexity of searching in a web operating system environment. We perform a simulation study using the Gridsim simulator, and our experiments show that our model provides enhanced utilization of resources, better search expressiveness, scalability, and precision.     

基于混合P2P网络模型的语义检索方法研究

在语义理解的基础上检索出满足用户需求的信息,是P2P走向更广泛应用的关键技术之一.提出了一种支持语义的混合P2P网络模型M-Chord,采用基于元数据规范模板(MST)的语义描述模型,结合Chord和语义覆盖网的技术特点,对基于MST的语义覆盖网动态生成方法进行了设计,提出了语义扩展路由的概念,并在上述研究的基础上提出了语义检索方法.通过实验分析表明,M-Chord具有较好的扩展性和语义检索性能.     

基于P2P的结构化半分布式语义搜索算法

目前的搜索引擎算法大多是基于关键词搜索,体系上是集中式结构,在安全性和语义性上存在缺陷.基于P2P的结构化半分布式语义搜索算法--DPSS(Distributed P2P Semantic Search),通过研究词与词的关联度,在传统的P2P覆盖语义层,实现语义功能.同时,结合文章距离算法,能够应用在文本分类、文章聚类等领域.