基于组件的多层数据库应用设计

因特网技术的快速发展扩展了多层计算模式的应用范围，由Web服务器、应用服务器和数据库服务器形成的多层数据库模型形成了目前因特网应用的骨干。使用CORBA技术构建多层分布式系统已经成为当前的主流技术，它大大降低了健壮的、大规模企业级系统的开发复杂度。     

An SSL Back-End Forwarding Scheme in Cluster-Based Web Servers

State-of-the-art cluster-based data centers consisting of three tiers (Web server, application server, and database server) are being used to host complex Web services such as e-commerce applications. The application server handles dynamic and sensitive Web contents that need protection from eavesdropping, tampering, and forgery. Although the secure sockets layer (SSL) is the most popular protocol to provide a secure channel between a client and a cluster-based network server, its high overhead degrades the server performance considerably and, thus, affects the server scalability. Therefore, improving the performance of SSL-enabled network servers is critical for designing scalable and high-performance data centers. In this paper, we examine the impact of SSL offering and SSL-session-aware distribution in cluster-based network servers. We propose a back-end forwarding scheme, called ssl_with_bf, that employs a low-overhead user-level communication mechanism like virtual interface architecture (VIA) to achieve a good load balance among server nodes. We compare three distribution models for network servers, round robin (RR), ssl_with_session, and ssl_with_bf, through simulation. The experimental results with 16-node and 32-node cluster configurations show that, although the session reuse of ssl_with_session is critical to improve the performance of application servers, the proposed back-end forwarding scheme can further enhance the performance due to better load balancing. The ssl_with_bf scheme can minimize the average latency by about 40 percent and improve throughput across a variety of workloads.     

A survey on dynamic Web content generation and delivery techniques

While Web applications serve personal needs and business functions almost in every area, the responsiveness and performance of Web applications is the key factor to their success. With continuous innovation on Web technology, Web sites have evolved from document Web to application Web and further to service Web recently. During the evolution course, Web sites serving dynamic content started to grow exponentially to dominate the area. Dynamic pages require servers to generate the response content per-user request before delivering it back to the user, which introduces network traffic, server workload and results in extra latency. This drew tremendous efforts from both research and industry on how to accelerate the dynamic content generation and distribution in order to reduce the user perceived latency and improve the application performance, among which caching is a vital technology. This paper attempts to survey the innovative research and products recently published in this area and presents them in a road map style. It first examines the dynamic characteristics of Web applications and the inherent challenges for caching. Then the rest of this paper explores the varied acceleration solutions on content generation process and content delivery process, respectively, followed by the analysis of how different caching solutions fit Web applications of different characteristics. Finally it ends with the future trends on Web caching technique and a summary of the survey.     

Providing scalable Web services using multicast communication

The recent growth in use of the World-Wide Web in the Internet has caused a significant increase in the demand placed on Web servers. This increased load results in noticeably longer response times for users. We propose an approach to using multicast in the delivery of Web resources that reduces the load on servers as well as the networks that connect them. We analyze the issues involved in using multicast in the Web, especially those related to routing and addressing, and present an alternative approach to multicast routing that is appropriate for this application. We also describe the design and implementation of a system based on the existing WWW client and server architecture and the multicast support provided within IP. Experimental results from this implementation are presented.     

Applications of a Web query language

In this paper we report on our experience using WebSQL, a high level declarative query language for extracting information from the Web. WebSQL takes advantage of multiple index servers without requiring users to know about them, and integrates full-text with topology-based queries.The WebSQL query engine is a library of Java classes, and WebSQL queries can be embedded into Java programs much in the same way as SQL queries are embedded in C programs. This allows us to access the Web from Java at a much higher level of abstraction than bare HTTP requests.We illustrate the use of WebSQL for application development by describing two applications we are experimenting with: Web site maintenance and specialized index construction. We also sketch several other possible applications.Using the library, we have also implemented a client-server architecture that allows us to perform interactive intelligent searches on the Web from an applet running on a browser.     

JPernLite: extensible transaction services for the WWW

Concurrency control is one of the key problems in design and implementation of collaborative systems such as hypertext/hypermedia systems, CAD/CAM systems, and software development environments. Most existing systems store data in specialized databases with built-in concurrency control policies, usually implemented via locking. It is desirable to construct such collaborative systems on top of the World Wide Web, but most Web servers do not support even conventional transactions, let alone distributed (multi-Website) transactions or flexible concurrency control mechanisms oriented toward team work-such as event notification, shared locks, and fine granularity locks. We present a transaction server that operates independently of Web servers or the collaborative systems, to fill the concurrency control gap. By default, the transaction server enforces the conventional atomic transaction model, where sets of operations are performed in an all-or-nothing fashion and isolated from concurrent users. The server can be tailored dynamically to apply more sophisticated concurrency control policies appropriate for collaboration. The transaction server also supports applications employing information resources other than Web servers, such as legacy databases, CORBA objects, and other hypermedia systems. Our implementation permits a wide range of system architecture styles     

Content delivery networks: status and trends

CDNs improve network performance and offer fast and reliable applications and services by distributing content to cache servers located close to users. The Web's growth has transformed communications and business services such that speed, accuracy, and availability of network-delivered content has become absolutely critical - both on their own terms and in terms of measuring Web performance. Proxy servers partially address the need for rapid content delivery by providing multiple clients with a shared cache location. In this context, if a requested object exists in a cache (and the cached version has not expired), clients get a cached copy, which typically reduces delivery time. CDNs act as trusted overlay networks that offer high-performance delivery of common Web objects, static data, and rich multimedia content by distributing content load among servers that are close to the clients. CDN benefits include reduced origin server load, reduced latency for end users, and increased throughput. CDNs can also improve Web scalability and disperse flash-crowd events. Here we offer an overview of the CDN architecture and popular CDN service providers.     

QCWS: an implementation of QoS-capable multimedia web services

QoS (Quality of Service), which defines service quality such as latency, availability, timeliness and reliability, is important for web applications that provide real-time information, multimedia content, or time-critical services. Many web applications are best implemented by servers with a guaranteed server processing capacity. In this research, we study the QoS control issues using the current Web services standards. We propose a QoS-capable Web service architecture, QCWS, by deploying a QoS broker between Web service clients and providers. The functions of the QoS broker module include tracking QoS information about servers, making selection decisions for clients, and negotiating with servers to get QoS agreements. We have implemented a QCWS prototype using IBM WSDK, enhanced with simple QoS capabilities. We have measured the performance running under different service priorities.     

一种轻量级Web服务组合研究与应用

Web服务作为一种新兴的Web应用模式受到了软件工程领域的广泛关注，其提供了一个解决异构平台上的应用之间连接、集成和互操作的技术框架。Web服务组合是将多个服务组合成一个能完成复杂商业任务的技术。该文给出了一种基于SOAP/WSDL的轻量级Web服务组合构架，用其解决了三峡—葛洲坝水利枢纽通航调度项目中异构平台上的数据和应用的整合与共享问题。     

基于敏感数据加密的分布式安全数据库服务研究*

针对目前基于数据加密技术的安全数据库服务不能有效平衡数据处理性能与数据隐私保护的不足,提出一种新的基于分布式安全数据库服务的隐私保护方法,通过引入准标志属性集的自动检测技术,采用对部分敏感属性加密和分解准标志属性集的方式实现数据的垂直分解,通过基于元数据的查询分解实现分布式查询处理。实验结果表明,该方法能较好地平衡查询性能与隐私保护之间的矛盾。     

A web services-based approach to develop a networked information integration service platform for gear enterprise

In order to deal with the problems of information integration and data sharing across distributed heterogeneous application systems in gear enterprises, it is imperative to build up a high quality information integration platform. Web Services, an emerging form of service-oriented architecture (SOA) for distributed computing, have the potential to serve as a key enabling technology to integrate heterogeneous systems under the distributed environment. This paper presents a novel information integration service platform which offers better support for the networked manufacturing of gear enterprise by taking full advantage of technologies of SOA and Web services. In this paper, the information integrated operation mode of gear enterprise networked manufacturing is deeply analyzed and the functional architecture of the networked information integration service platform is proposed. Furthermore, the application integrated framework of gear enterprise is constructed and the software architecture of the service platform is implemented in the .NET environment. Finally, an actual application example of hypoid gear networked manufacturing is provided to demonstrate the practicability of the proposed platform.     

The implementation of a secure and pervasive multimodal Web system architecture

While most users currently access Web applications from Web browser interfaces, pervasive computing is emerging and offering new ways of accessing Internet applications from any device at any location, by utilizing various modes of interfaces to interact with their end users. The PC and its back-end servers remain important in a pervasive system, and the technology could involve new ways of interfacing with a PC and/or various types of gateways to back-end servers. In this research, cellular phone was used as the pervasive device for accessing an Internet application prototype, a multimodal Web system (MWS), through voice user interface technology.This paper describes how MWS was developed to provide a secure interactive voice channel using an Apache Web server, a voice server, and Java technology. Securing multimodal applications proves more challenging than securing traditional Internet applications. Various standards have been developed within a context of Java 2 Micro Edition (J2ME) platform to secure multimodal and wireless applications. In addition to covering these standards and their applicability to the MWS system implementation, this paper also shows that multimodal user-interface page can be generated by using XSLT stylesheet which transforms XML documents into various formats including XHTML, WML, and VoiceXML.     

用MPLS实现的可伸缩Web请求路由

对相关Web分配器技术进行分析，并提出一个新颖的构架来改进在服务器和缓存集群中Web请求路由，MPLS方案利用应用层信息到第二层标签以提高复杂的请求路由功能，而不会发生TCP连接终止瓶颈。需要客户端代理服务器参与为客户请求申请到合适的标签，可用off-the-shelf MPLS交换去执行分配。允许分配器执行一些关健功能实现可伸缩性。     

Natural-language understanding at BBN

Natural-language understanding has evolved from its earliest days in which scientists use an early approach to parsing, to more sophisticated techniques that enable systems to extract information from open-domain text sources to fill data bases automatically. Natural language processing has many potential applications, such as translating foreign-language documents on the Web; automatically routing questions to an appropriate expert at a help/service telephone number; fully automatic question answering; delivering answers to a Web query, as opposed to delivering pointers to Web pages; and automatically filling a structured database with desired information from text or speech sources.     

A performance study of robust load sharing strategies fordistributed heterogeneous Web server systems

Replication of information across multiple servers is becoming a common approach to support popular Web sites. A distributed architecture with some mechanisms to assign client requests to Web servers is more scalable than any centralized or mirrored architecture. In this paper, we consider distributed systems in which the Authoritative Domain Name Server (ADNS) of the Web site takes the request dispatcher role by mapping the URL hostname into the IP address of a visible node, that is, a Web server or a Web cluster interface. This architecture can support local and geographical distribution of the Web servers. However, the ADNS controls only a very small fraction of the requests reaching the Web site because the address mapping is not requested for each client access. Indeed, to reduce Internet traffic, address resolution is cached at various name servers for a time-to-live (TTL) period. This opens an entirely new set of problems that traditional centralized schedulers of parallel/distributed systems do not have to face. The heterogeneity assumption on Web node capacity, which is much more likely in practice, increases the order of complexity of the request assignment problem and severely affects the applicability and performance of the existing load sharing algorithms. We propose new assignment strategies, namely adaptive TTL schemes, which tailor the TTL value for each address mapping instead of using a fixed value for all mapping requests. The adaptive TTL schemes are able to address both the nonuniformity of client requests and the heterogeneous capacity of Web server nodes. Extensive simulations show that the proposed algorithms are very effective in avoiding node overload, even for high levels of heterogeneity and limited ADNS control     

Virtualization-based autonomic resource management for multi-tier Web applications in shared data center

As large data centers emerge, which host multiple Web applications, it is critical to isolate different application environments for security reasons and to provision shared resources effectively and efficiently to meet different service quality targets at minimum operational cost. To address this problem, we developed a novel architecture of resource management framework for multi-tier applications based on virtualization mechanisms. Key techniques presented in this paper include (1) establishment of the analytic performance model which employs probabilistic analysis and overload management to deal with non-equilibrium states; (2) a general formulation of the resource management problem which can be solved by incorporating both deterministic and stochastic optimizing algorithms; (3) deployment of virtual servers to partition resource at a much finer level; and (4) investigation of the impact of the failure rate to examine the effect of application isolation. Simulation experiments comparing three resource allocation schemes demonstrate the advantage of our dynamic approach in providing differentiated service qualities, preserving QoS levels in failure scenarios and also improving the overall performance while reducing the resource usage cost.     

基于Windows Mobile平台对异构数据库Oracle的访问

Oracle数据库是许多成熟应用系统采用的比较多的后台数据库,在对这些系统开发基于Windows Moble平台的移动应用时对异构数据库Oracle的访问是必须解决问题.本文介绍了一种在Windows Mobile上通过Web service访问Oracle数据库的方法.     

一种CDN中的动态数据存储方案——UbDP

CDN对于动态Web应用的加速通常采用数据缓存或复制技术。针对论坛、博客服务提供商等为注册用户提供个人信息发布平台的网站,提出了一种基于用户的数据分割方法：将数据按所属注册用户进行分割,分布到离该用户最近的数据库系统中。将数据库UID操作分散到多个数据库系统,消除了单个数据库系统的I/O瓶颈。     

Reconfigurable Service Composition and Categorization for Power-Aware Mobile Computing

The requirement of agile adaptation to varying resource constraints in mobile systems motivates the use of a service-oriented architecture (SOA), which can support the composition of two or more services to form a complex service. In this paper, we propose SOA-based middleware to support QoS control of mobile applications and to configure an energy-efficient service composition graph. We categorize services into two layers:functionality-centric services, which are connected to create a complex service to meet the user's intentions, and resource-centric services, which undertake distributed functionality-centric services in a way that increases the success rate of service composition while reducing contention at specific service nodes. We also present a service routing algorithm to balance the resource consumption of service providers on a service-overlay network. Through simulation of power-aware service composition using a realistic model based on ns-2 and traced data, we demonstrate that our approach can help both the mobile devices and the servers in a service-overlay network to reduce energy consumption without an increase in response time.     

基于XML的异构数据交换技术的研究

随着电子政务的不断发展,政府的各个部门间需要交换的数据日益繁重,因此,基于电子政务的异构数据交换技术的研究显得格外重要。论文提出了基于XML的异构数据交换技术,使用XML可以将来自异构系统的不同数据源的数据很容易的集成在一起,应用软件可以在中间层的服务器上对后台数据库的数据进行集成,然后以XML格式发送给客户端或其他服务器。客户端在接收到数据以后,可以使用本地软件来解析数据,并对数据作进一步处理,这样就能有效地解决网络中日益繁重的异构数据交换问题。