数字图书馆包装层生成技术研究     

张付志  肖阳 《中国图书馆学报》2006,32(4)

包装层是对应于特定信息源的一种特殊程序,是实现异构信息源集成的关键。数字图书馆的包装层可以作为数字图书馆的智能前端代理,负责把来自中介层的统一查询表示映射为针对具体数字图书馆的查询格式,并从得到的查询结果中提取出用户需要的信息,提交给中介层。数字图书馆包装层生成的关键技术主要有:查询映射机制,查询服务调用机制,结果提取与转换机制。图6。参考文献5。  相似文献   

Two-stage statistical language models for text database selection   总被引：2，自引：0，他引：2  

Hui Yang  Minjie Zhang 《Information Retrieval》2006,9(1):5-31

As the number and diversity of distributed Web databases on the Internet exponentially increase, it is difficult for user to know which databases are appropriate to search. Given database language models that describe the content of each database, database selection services can provide assistance in locating databases relevant to the information needs of users. In this paper, we propose a database selection approach based on statistical language modeling. The basic idea behind the approach is that, for databases that are categorized into a topic hierarchy, individual language models are estimated at different search stages, and then the databases are ranked by the similarity to the query according to the estimated language model. Two-stage smoothed language models are presented to circumvent inaccuracy due to word sparseness. Experimental results demonstrate that such a language modeling approach is competitive with current state-of-the-art database selection approaches.  相似文献   

The Co-Effects of Query Structure and Expansion on Retrieval Performance in Probabilistic Text Retrieval     

Jaana Kekäläinen  Kalervo Järvelin 《Information Retrieval》2000,1(4):329-344

The effects of query structures and query expansion (QE) on retrieval performance were tested with a best match retrieval system (InQuery¹). Query structure means the use of operators to express the relations between search keys. Six different structures were tested, representing strong structures (e.g., queries with facets or concepts identified) and weak structures (no concepts identified, a query is a bag of search keys). QE was based on concepts, which were first selected from a searching thesaurus, and then expanded by semantic relationships given in the thesaurus. The expansion levels were (a) no expansion, (b) a synonym expansion, (c) a narrower concept expansion, (d) an associative concept expansion, and (e) a cumulative expansion of all other expansions. With weak structures and Boolean structured queries, QE was not very effective. The best performance was achieved with a combination of a facet structure, where search keys within a facet were treated as instances of one search key (the SYN operator), and the largest expansion.  相似文献   

Z39.50客户机和服务器的实现   总被引：2，自引：0，他引：2  

薛锋  郑巧英  杨宗英 《大学图书馆学报》2000,18(4):35-40

对在TCP/IP协议上实现Z39.5 0客户机和服务器所涉及到的主要问题进行了研究 ,给出了一个相应的解决方案 ,并介绍了自行开发的Z39.5 0客户机软件和服务器软件  相似文献   

Das MINERVA-Projekt: Datenbankselektion für Peer-to-Peer-Websuche     

Matthias Bender  Sebastian Michel  Gerhard Weikum und Christian Zimmer 《Informatik - Forschung und Entwicklung》2005,20(3):152-166

Zusammenfassung In diesem Artikel wird MINERVA pr?sentiert, eine prototypische Implementierung einer verteilten Suchmaschine basierend auf einer Peer-to-Peer (P2P)-Architektur. MINERVA setzt auf die in der P2P-Welt verbreitete Technik verteilter Hash-Tabellen auf und benutzt diese zum Aufbau eines verteilten Verzeichnisses. Peers in unserem Ansatz entsprechen v?llig autonomen Benutzern mit ihren lokalen Suchm"oglichkeiten, die bereit sind, ihr lokales Wissen und ihre lokalen Suchm?glichkeiten im Rahmen einer Kollaboration zur Verfügung zu stellen. Wir formalisieren unsere Systemarchitektur und beschreiben das zentrale Problem einer effizienten Suche nach vielversprechenden Peers für eine konkrete Anfrage innerhalb des Verbundes. Wir greifen dabei auf existierende Methoden zurück and passen diese an unseren Systemkontext an. Wir pr?sentieren Experimente auf realen Daten, die verschiedene dieser Ans?tze vergleichen. Diese Experimente zeigen, dass die Qualit?t der Ans?tze variiert und untermauern damit die Wichtigkeit und den Einfluss einer leistungsstarken Methode zur Auswahl guter Datenbanken. Unsere Experimente deuten an, dass eine geringe Anzahl sorgf?ltig ausgew?hlter Datenbanken typischerweise bereits einen Gro?teil aller relevanten Ergebnisse des Gesamtsystems liefert.

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This paper presents the MINERVA project that protoypes a distributed search engine based on P2P techniques. MINERVA is layered on top of a Chord-style overlay network and uses a powerful crawling, indexing, and search engine on every autonomous peer. We formalize our system model and identify the problem of efficiently selecting promising peers for a query as a pivotal issue. We revisit existing approaches to the database selection problem and adapt them to our system environment. Measurements are performed to compare different selection strategies using real-world data. The experiments show significant performance differences between the strategies and prove the importance of a judicious peer selection strategy. The experiments also present first evidence that a small number of carefully selected peers already provide the vast majority of all relevant results.

CR Subject Classification H.4,H.3.3,H3.4  相似文献   

关于《中华人民共和国劳动合同法》的几个问题     

王巧玲 《山东商业职业技术学院学报》2008,8(4):64-66

《劳动合同法》于2008年1月1日正式生效,伴随着它的实施,出现了一系列问题,许多用人单位和劳动者产生众多的困惑,甚至有人认为：《劳动合同法》是对《劳动法》的修改。许多用人单位认为：该法过多地保护了劳动者的权益。也有个别的用人单位全然不把《劳动合同法》的规定当回事,现实中,违法用工的情况时有发生,为此,本文对《劳动合同法》做了几点说明。  相似文献   

微博问政对我国政策制定的影响     

骆海明 《邢台职业技术学院学报》2013,30(2):69-72

微博问政是网络问政的一种新形式。在政策制定中,微博问政拓展了公民参与政策制定的公共空间,微博议题成为了公共问题,博民平等参与有利于塑造理性决策制定者。然而,微博问政必然带有缺陷,因而需要政府和公众两个层面改进。从政府角度通过加大信息公开来保障公民参政权利,加大制度建设来构建微博问政平台;从公民角度提高公民意识,增强公共舆论理性。  相似文献   

1数学建模在供应链管理教学中的应用     

翁克瑞 《科教文汇》2012,(19):40-41

近年来,供应链管理优化成为研究热点,但在本科教学中很少涉及。这是因为供应链管理优化方法往往涉及复杂的求解算法和编程技术,受教学时间和数学基础限制,普通本科生往往很难掌握。为此,本文提出在供应链管理教学中介绍数学建模技术,用数学模型表示供应链管理优化问题,再用商业软件求解,可以减少学习难度,提高学生的操作能力。本文介绍了供应链管理中涉及数学建模的教学内容,然后以生产批量优化模型为例,说明这一教学方式的应用。  相似文献   

Document replication strategies for geographically distributed web search engines     

Enver Kayaaslan  B. Barla Cambazoglu  Cevdet Aykanat 《Information processing & management》2013

Large-scale web search engines are composed of multiple data centers that are geographically distant to each other. Typically, a user query is processed in a data center that is geographically close to the origin of the query, over a replica of the entire web index. Compared to a centralized, single-center search engine, this architecture offers lower query response times as the network latencies between the users and data centers are reduced. However, it does not scale well with increasing index sizes and query traffic volumes because queries are evaluated on the entire web index, which has to be replicated and maintained in all data centers. As a remedy to this scalability problem, we propose a document replication framework in which documents are selectively replicated on data centers based on regional user interests. Within this framework, we propose three different document replication strategies, each optimizing a different objective: reducing the potential search quality loss, the average query response time, or the total query workload of the search system. For all three strategies, we consider two alternative types of capacity constraints on index sizes of data centers. Moreover, we investigate the performance impact of query forwarding and result caching. We evaluate our strategies via detailed simulations, using a large query log and a document collection obtained from the Yahoo! web search engine.  相似文献   

免费师范生政策制定与执行的公共政策学角度分析     

刘佳 《四川教育学院学报》2012,28(4):10-13

公共政策的制定与执行是一个体现目的和价值的过程。通过从公共政策学的角度分析免费师范生政策的制定、执行过程,得出：在确定议程上政治领导人起了关键作用;政策规划者主要是行政部门、政策分析家,六所师范大学;政策规划符合公共政策规划的原则、程序,最终政策方案抉择是依靠行政命令;政策执行主体注重政策的操作化,建立了相应的组织负责政策执行,但政策宣传力不够,执行中免费师范生的生活补贴偏少;在部属师范大学实行免费师范生政策没有进行过提前政策实验,政策执行以行政手段为主。  相似文献