共查询到19条相似文献,搜索用时 171 毫秒
1.
因特网的不断发展使得XML成为Web上数据交换和表示的标准格式,但是大量的商业数据仍然存储在关系数据库中。因此必须将关系数据发布成XML文档进行传输。提出了一种基于分层框架结构的关系数据库向XML的映射方法,并在分层结构中定义了一种XML模式图作为XML的概念模型。得到的XML文档能够很好地反映关系数据库的语义和各种约束并且没有引入数据冗余。初步实验结果表明方法具有较高的效率和较好的准确性。 相似文献
2.
集中管理式Web缓存系统及性能分析 总被引:5,自引:0,他引:5
共享缓存文件是减少网络通信量和服务器负载的重要方法,本文在介绍Web Caching技术及流行的Web缓存通信协议ICP的基础上,提出了一种集中管理式Web缓存系统,该系统通过将用户的HTTP请求,按照一定的算法分发到系统中某一合适的缓存服务器上,从而消除了缓存系统内部服务器之间庞大的通信开销及缓存处理负担,减少了缓存内容的冗余度.通过分析,证明了集中管理式Web缓存系统比基于ICP的简单缓存系统具有缓存效率高、处理开销低、延迟小等优点,并且该系统具有良好的可扩展性. 相似文献
3.
介绍了提高Web服务器性能的前沿技术--分布式Web服务器系统,讨论了现有各种方案的优缺点,在此基础上提出一种新的分布式Web服务器系统.该系统使用基于标记的缓存协作用户请求分发方法(tag based cache cooperative Web requests distribution,简称TB-CCRD),通过前端机把系统中各个Web服务器的缓存组织成一个大的虚拟缓存系统,提高系统的整体缓存命中率,缩短了请求的响应时间;通过分布式处理TCP连接转交来消除前端机的性能瓶颈;利用标记通告URL在缓存中的位置,避免了额外的系统内部通信.从而得到了一个可扩展的高性能分布式Web服务器系统. 相似文献
4.
Ajax技术及其Web开发 总被引:1,自引:0,他引:1
Ajax开发Web具有无需重新装载整个页面便能向服务器发送请求和对XML文档的解析和处理两项强大的性能,它在用户与处理器之间引入一个中间媒介,使得Web应用更加动态,不必完全依赖于从服务器重新载入页面来向用户呈现更改. 相似文献
5.
针对网络和移动计算环境下Web信息集成系统中XML数据查询处理的瓶颈,提出了一种基于SAT和TRT的语义缓存以及for和return子句的重写规则,有效地缩短Web信息查询响应时间。 相似文献
6.
7.
Web缓存分层结构在避免单点失效、提高缓存性能方面具有重要作用.论文研究了Web缓存层次模型,提出请求分发的三种模式,并利用代价函数分析探讨了缓存模型性能.根据Web访问共同特征,实验采用数学建模方法生成模拟日志,模拟不同层采用不同替换算法(LRU、LFU、GDS)时的缓存性能.结果表明,模拟日志的高频区、低频区流行度访问特征分别服从齐普夫第一定律、第二定律,具有真实日志的特性,能够模拟用户请求评价Web缓存层次模型性能;当低层代理缓存采用LFU或LRU替换算法,高层代理缓存采用GDS替换算法时,两层缓存模型在命中率、字节命中率方面有较好的性能表现. 相似文献
8.
阐述了Web Service技术,提出了基于XML和Web Service实现野外试验站信息发布平台以及实现平台关键技术的研究。 相似文献
9.
10.
WSRF规范迈出了将网格技术和Web服务技术加以融合的关键一步,服务调用性能的重要性日益突出,服务网关最初用于解决公共IP和私有IP之间的Web服务可访问性问题,现在也用于基于集群的Web服务的调度,本文结合Web服务和网格中常见的数据服务和信息服务的特性,在服务网关中引入了一种新颖的虚拟服务缓存模型,并通过定量的分析,证明该模型能够有效缩短可缓存服务的平均响应时间.实验表明,该虚拟服务缓存模型,具有普遍性,并且可以有效地缩短服务的平均响应时间. 相似文献
11.
XML has been the de‐facto standard of information representation and exchange over the web. As the next generation of the Web language, XML is straightforwardly usable over the Internet. At the same time, the real world is filled with imprecision and uncertainty. However, the existed works fall short in their ability to model imprecise and uncertain data using XML. In this paper, we propose a new fuzzy XML data model based on XML Schema. With the model used, the fuzzy information in XML documents can be represented naturally. Along with the model, an associated algebra is presented formally. We also introduce how to use our algebra to capture queries expressed in XQuery. It shows that this model and algebra can establish a firm foundation for publishing and managing the histories of fuzzy data on the Web. © 2010 Wiley Periodicals, Inc. 相似文献
12.
XML has become the standard for publishing and exchanging data on the Web. However, most business data is managed and will
remain to be managed by relational database management systems. As such, there is an increasing need to efficiently and accurately
publish relational data as XML documents for Internet-based applications. One way to publish relational data is to provide
virtual XML documents for relational data via an XML schema which is transformed from the underlying relational database schema
such that users can access the relational database through the XML schema. In this paper, we discuss issues in transforming
a relational database schema into the corresponding XML schema. We aim to preserve all integrity constraints defined in a
relational database schema, to achieve high level of nesting and to avoid introducing data redundancy in the transformed XML
schema. In the paper, we first propose a basic transformation algorithm which introduces no data redundancy, then we improve
the algorithm by exploring further nesting of the transformed XML schema. 相似文献
13.
基于关系数据库的XML数据管理 总被引:15,自引:0,他引:15
Currently,there are a great of research topics that focus on storing and querying XML data in an RDBMS,and publishing relational data as XML documents ,and querying XML views of relational data. An overview of XML data management based on RDBMS is given in this paper. Some existing technologies of storing and querying XML data in relational databases ,publishing relational data as XML documents ,and querying XML views of relational dataare sufficiently surveyed,their advantages ,disadvantages ,and causes are analyzed. 相似文献
14.
研究了数据库查询优化问题,而XISS索引是XML数据库索引中支持正则路径表达式的典型代表。XISS索引对于长查询路径表达式,要产生大量中间结果,连接操作代价十分高,加大了查询的时间和空间复杂度,导致查询的效率和准确率低。为了提高XML数据库查询效率和准确率,提出一种改进的XISS索引技术。首先引入DTD模式信息,简化编码方式;然后对节点索引结构进行改进,减少中间结果的连接次数,使得查询时间与路径长度无关,提高了查询效率和准确率。最后通过实验对改进前后的XISS索引进行仿真。结果表明,改进的XISS索引缩短了建立索引的时间,加快了查询响应的速度,提高了XML数据库查询的效率和准确率。 相似文献
15.
16.
17.
Maged El-Sayed Katica Dimitrova Elke A. Rundensteiner 《Data & Knowledge Engineering》2005,54(3):355-390
XML is an ordered data model and XQuery expressions return results that have a well-defined order. However, little work on how order is supported in XML query processing has been done to date. In this paper we study the issues related to handling order in the XML context, namely challenges imposed by the XML data model, the variety of order requirements of the XQuery language, and the need to maintain order in the presence of updates to the XML data. We propose an efficient solution that addresses all these issues. Our solution is based on a key encoding for XML nodes that serves as node identity and at the same time encodes order. We design rules for encoding order of processed XML nodes based on the XML algebraic query execution model and the node key encoding. These rules do not require any actual sorting for intermediate results during execution. Our approach enables efficient order-sensitive incremental view maintenance as it makes most XML algebra operators distributive with respect to bag union. We prove the correctness of our order encoding approach. Our approach is implemented and integrated with Rainbow, an XML data management system developed at WPI. We have tested the efficiency of our approach using queries that have different order requirements. We have also measured the relative cost of different components related to our order solution in different types of queries. In general the overhead of maintaining order in our approach is very small relative to the query processing time. 相似文献
18.
XML has become the standard for publishing and exchanging data on the Web. Since most of the business data nowadays are stored in structured databases including relational and object-oriented databases (OODB), it is of significance to automate the transformation process and generate the XML data containing information from existing databases. At the same time, information imprecision and uncertainty exist in many practical applications, and for this reason, fuzzy data modeling has been extensively investigated in various data models. As such, there is an increasing need to effectively publish fuzzy structured data as fuzzy XML documents for Web-based applications. In this paper, we take a significant step in a fundamental consolidation of fuzzy XML. In particular, we are interested in finding an XML schema that best describes the existing fuzzy object-oriented schema. To accomplish this, we first offer mapping formalisms to capture the semantics of fuzzy XML Schema and fuzzy object-oriented schema. To allow for better and platform independent sharing of data stored in an object-oriented format, we investigate the formal transformation from fuzzy OODB to fuzzy XML and develop a set of rules to assist in the transformation process. 相似文献
19.
在医院信息集成系统中,集成来自各医院的医疗数据是上级领导机关进行分析和决策的基础。由于各医院系统数据异构性很大,且医疗数据每天都在更新,将不同数据源的医疗数据增量发布成统一的XML格式,然后通过网络传输到中心服务器进行增量更新是系统数据集成的有效手段。但XML天生具有数据冗余量大的缺点,对网络传输的要求很高,当数据量很大时,集成系统的处理效率不高。XML数据压缩是解决XML数据体积过大问题的有效手段。本文针对医疗数据的这一特点,提出了一种无需文档类型定义的XML数据压缩算法XCompress,实验证明它具有压缩比率大、压缩时间短的优点,能够有效地对医院信息集成系统中的XML数据进行压缩,大大减小了网络传输的时间与负载,提高了系统的运行效率。 相似文献