基于三层结构的数据通道思想及其应用

通过分析、研究C／S、B／S和三层（多层）结构的特点，提出了一种基于三层结构的数据通道思想，并将数据通道技术应用到高校科研管理系统中。利用数据通道技术，Web用户不直接访问数据库，而是通过Web服务器来访问应用程序，通过应用程序的执行来访问数据库，从而提高了数据库的安全性。由于在Web服务器与数据库服务器之间不存在平台，只进行通信，因此实现起来简单、快捷。     

用PB8的Web Data Windows DTC开发Web应用

浏览器／Web服务器 应用服务器／数据库服务器的三层或多层体系结构已成为当今应用开发技术的主流，本文着重介绍PowerBuilder8．0的Web Data Window DTC的使用，阐述瘦客户技术的实现。     

利用JDBC实现基于Internet的网上答疑系统

介绍了一个利用ＪＤＢＣ实现的基于“客户机－Ｗｅｂ服务器－数据库服务器”三层体系结构的因特网上答疑系统。系统的功能设计方便,有效,在实现上选用了新兴网络编程语言ＪＡＶＡ及其数据库连接技术ＪＤＢＣ,使系统可在不同的软硬件平台上顺畅运行;管理和使用也非常方便灵活,只需因特网上的通用浏览器软件即可,具有一定的推广价值。     

提高分布式多层系统执行效率方法的研究

分布式多层系统由客户端应用程序、应用服务器层、数据库服务器层构成。由于分布式多层应用系统均在网络环境下运行，所以，它的执行效率成为设计时不可忽视的重点。以提高分布式多层应用系统的执行效率为目的，文中总结了如何使用Delphi所提供的相关技术来提高分布式多层MIS系统执行效率的几种方法。并得出结论：合理地运用Delphi所提供的相关技术可以大幅度提高分布式多层应用系统的执行效率。     

利用JDBC实现基于Internet的网上答疑系统

介绍了一个利用JDBC实现的基于“客户机-Web服务器-数据库服务器”三层体系结构的因特网上答疑系统。系统的功能设计方便、有效,在实现上选用了新兴网络编程语言JAVA及其数据库存连接技术JDBC,使系统可在不同的软硬件平台上顺畅运行;管理和使用也非常方便、灵活,只需因特网上的通用浏览器软件即可,具有一定的推广价值。     

定制标识在多层Web数据库系统中的应用

针对如何构建高性能的网络应用系统,合理利用现有网络资源,提高工作效率的问题,通过把数据库和Web技术结合,来实现网络信息的动态发布和网络办公自动化。介绍了定制HTML标识的作用和工作机理,结合WebBmker技术讨论了在多层Web数据库应用系统中数据层、应用程序服务器、界面层是如何实现数据库数据的动态传递的,并结合实际介绍了多层Web应用系统的具体实现过程。     

基于三层结构的数据通道思想及其应用

通过分析、研究C/S、B/S和三层(多层)结构的特点,提出了一种基于三层结构的数据通道思想,并将数据通道技术应用到高校科研管理系统中。利用数据通道技术,Web用户不直接访问数据库,而是通过Web服务器来访问应用程序,通过应用程序的执行来访问数据库,从而提高了数据库的安全性。由于在Web服务器与数据库服务器之间不存在平台,只进行通信,因此实现起来简单、快捷。     

MIDAS在机动车安全性能测控管理系统中的应用

MIDAS是Delphi为开发多层应用系统提供的透明中介引擎，在对MIDAS技术进行分析和研究后，将其应用到了机动车安全性能测控分布式管理系统中。利用MIDAS将该系统设计成三层的结构，即在数据库服务器和客户机之间增加了应用程序服务器。使得客户机与数据库的连接、客户机对数据库的操作都由作为中间层的应用程序服务器完成。利用MIDAS的自动化功能还设计了一种客户机之间共享信息管理机制，从而增强了系统的安全性、可维性，提高了系统的运行效率。     

基于Web的多层客户／服务器数据库应用程序

讨论基于Web的多层客户／服务器数据库应用计算模型,并提出采用Delphi建立基于Web的多层客户／服务器数据库应用程序的方法和步骤。     

用PB8的Web DataWindow DTC开发Web应用

浏览器/Web服务器+应用服务器/数据库服务器的三层或多层体系结构已成为当今应用开发技术的主流,本文着重介绍 PowerBuilder 8.0的 Web Data Window DTC的使用,阐述瘦客户技术的实现。     

Tuning mechanisms for two major parameters of Apache web servers

Apache web servers are widely used as stand‐alone servers or front‐ends in multi‐tiered web servers. Despite the wide availability of software, it is quite difficult for many administrators to properly configure their web servers. In particular, setting the performance‐related parameters is an error‐prone and time‐consuming task because their values heavily depend on the server environment. In this paper, two mechanisms are described for automatically tuning two performance‐related parameters of Apache web servers: KeepAliveTimeout and MaxClients . These mechanisms are easy to deploy because no modifications to the server or the operating system are required. Moreover, they are parameter specific. Although interference between KeepAliveTimeout and MaxClients is inevitable, the tuning mechanisms minimize the correlation by using almost completely independent metrics. Experimental results show that these mechanisms work well for two different workloads; the parameter values are close to optimal and can adapt to workload changes. Copyright © 2007 John Wiley & Sons, Ltd.     

A Tiered System for Serving Differentiated Content

Contemporary Web sites typically consist of front–end Web servers, application servers, and back-end information systems such as database servers. There has been limited research on how to provide overload control and service differentiation for the back-end systems. In this paper we propose an architecture called tiered service (TS) for these purposes. In TS, there are several heterogeneous back-end systems to serve the Web applications. The Web applications communicate with a routing intermediary to intelligently route the queries to the appropriate back-end servers based on various policies such as client profiles and server load. In our system the back ends may store different qualities of data; lower quality data typically requires less overhead to serve. The main contributions of this paper include (i) a tiered content replication scheme that replicates tiered qualities of data on heterogeneous back ends with different capacity to satisfy clients with diverse requirements for latency and quality of data, and (ii) an application-transparent query routing architecture that automatically routes the queries to the appropriate back ends. The architecture was implemented in our test bed, and its performance was benchmarked. The experimental results demonstrate that TS offers significant performance improvement.     

Internet环境下分布式网络个人助理系统设计与实现

在分布式Internet/Intranet网络环境下,信息与资源的广泛共享和分布、用户的移动性和业务的不确定性、网络终端的相对固定性等是信息系统建设中的几个矛盾因素。我们设计的分布式网络个人助理系统利用多层、分布式、构件化的思想,基于分布式网络环境,实现用户信息资源的集中管理,提供个性化服务,为办公自动化向计算机网络化的方向发展和移动计算提供示范性的开发手段和方法。     

Self‐adaptation of service level in distributed systems

Modern distributed systems are diverse and dynamic, and consequently difficult to manage using traditional approaches, which rely on an extensive initial knowledge of the system. On the performance front, these systems often offer multiple opportunities for dynamically degrading or improving service level based on workload intensity, to avoid overload and underload. In this context, we propose a novel approach for building distributed systems capable of autonomously deciding when and how to adapt service level. Our approach limits the knowledge that must be provided manually to a component‐based representation of the system. From this representation, we build and maintain a performance profile, which allows us to (1) identify the most promising adaptations based on workload type and (2) dynamically characterize the intrinsic efficiency of each adaptation based on past attempts. We have successfully implemented and evaluated a prototype of our approach in the context of multi‐tiered application servers. Copyright © 2010 John Wiley & Sons, Ltd.     

Understanding and Dealing with Common Peer-to-Peer (P2P) Application Security

Abstract

In the early days of the Internet, most computers had a clearly defined role: storage, computation, management, and identity were all responsibilities relegated to servers. This was due primarily to the fact that servers were capable of supporting these functions, and personal computers were capable of little more than running a browser. Additionally, servers were given a static address and name, and maintained a persistent connection to the Internet. In contrast to servers, most Internet-connected personal computers did not have a static identity on the Internet. That is, personal computers did not maintain a regular IP address, name, or persistent presence on the Internet. Based on the unreliable presence of personal computers on the Internet, these machines were incapable of sharing their computing resources to actively participate as a component of a larger system.     

面向云计算的数据中心网络体系结构设计

近年来,云计算技术的蓬勃发展为整个IT行业带来了巨大变革.传统数据中心网络拓扑构建方式及网络层控制平面的运行机制存在固化性,已经难以满足新形势下日益增长的高性能及高性价比需求,并且无法支持云环境下更加灵活的按带宽租赁数据中心网络的运营方式.因此,提出了一种通过低造价的可编程交换机来构建具有高连通性的非树状数据中心网络的方式,并设计了可编程交换机与服务器2.5层代理协同工作的基于凸优化的虚拟网络带宽控制管理机制,从而提供足够的灵活性以对资源虚拟化技术提供更好的支持.实验表明,新型体系结构在降低构建成本的同时大幅提高了数据中心网络的吞吐量并提供了更加灵活的网络带宽分配机制.     

Lightweight and Informative Traffic Metrics for Data Center Monitoring

In recent years, thousands of commodity servers have been deployed in Internet data centers to run large scale Internet applications or cloud computing services. Given the sheer volume of data communications between servers and millions of end users, it becomes a daunting task to continuously monitor the availability, performance and security of data centers in real-time operational environments. In this paper, we propose and evaluate a lightweight and informative traffic metric, streaming frequency, for network monitoring in Internet data centers. The power-series based metric that is extracted from the aggregated IP traffic streams, not only carries temporal characteristics of data center servers, but also helps uncover traffic patterns of these servers. We show the convergence and reconstructability properties of this metric through theoretical proof and algorithm analysis. Using real data-sets collected from multiple data centers of a large Internet content provider, we demonstrate its applications in detecting unwanted traffic towards data center servers. To the best of our knowledge, this paper is the first to introduce a streaming metric with a unique reconstruction capability that could aid data center operators in network management and security monitoring.     

HTTP多路超链接在WebServers中的应用

频繁的WWW访问要求有有效的WebServers组织方式,针对HTTP超链接不能进行负载平衡的缺点,提出了HTTP多路超链接,并用HTTP超链接对HTTP多路超链接进行了模拟,最后将HTTP多路超链接引入WebServers设计。     

Boolean similarity measures for resource discovery

As the number of Internet servers increases rapidly, it becomes difficult to determine the relevant servers when searching for information. The authors develop a new method to rank Internet servers for Boolean queries. Their method reduces time and space complexity from exponential to polynomial in the number of Boolean terms. They contrast it with other known methods and describe its implementation