Introducing QoS awareness in distributed programming: QTcl

A number of distributed applications require communication services with quality of service (QoS) guarantees. Building global‐scale distributed systems with predictable properties is one of the great challenges for computer systems engineering in the new century. Work undertaken within the Internet Engineering Task Force has led to the definition of novel architectural models for the Internet with QoS support. According to these models, the network has to be appropriately configured in order to provide applications with the required performance guarantees. In next‐generation networks, enabling applications to interact with the underlying QoS services is of primary importance. Hence, several special‐purpose application programming interfaces (APIs) have been defined to let applications negotiate QoS parameters across QoS‐capable networks. However, so far, none of these APIs are available in different operating environments. We believe that such features should be embedded in programming environments for distributed applications. In this work we present how we included QoS control features in Tcl, a programming language that has been widely adopted for the development of distributed multimedia applications. Our work has led to the implementation of QTcl, an extended Tcl interpreter that provides programmers with a new set of primitives, in full compliance with the standard SCRAPI programming interface for the RSVP protocol. QTcl in highly portable, in that it enables standard QoS negotiation to be performed in a seamless fashion on the most common operating systems. Copyright © 2003 John Wiley & Sons, Ltd.     

Web信息集成技术研究

信息系统集成技术已经历了二十多年的发展，研究者已提出了很多信息集成的体系结构和实现方案，然而这些方法研究的主要集成对象是传统的异构数据库系统。随着Internet的飞速发展，网络迅速成为一种重要的信息传播和交换的手段，尤其是Web上，有着及其丰富的数据来源。如何获取Web上的有用数据并加以综合利用，即构建Web信息集成系统，成为一个引起广泛关注的研究领域。本文结合自己的研究工作，对这一领域的研究做了简单的综述，对有关的研究问题给出了分析。     

基于动态工作流技术的智能办公自动化系统的研究

针对常见办公自动化系统智能程度低、自动化程度受到限制等问题，提出了“意见—路由支持系统”和建立在该系统基础之上的“智能办公自动化系统模型”、“智能化动态工作流参考模型”等。基于这些模型开发的办公自动化系统，不仅具备一定的智能，而且在自动化程度、柔性、通用性等方面都有所提高，开发的工作流管理系统还具有可移植性。     

Dynamic anti-windup based control method for state constrained systems

Based on the dynamic anti-windup strategy, an alternative control methodology for state constrained systems is presented. The proposed method is an a posteriori approach for state constrained systems, which is differentiated from the usual a priori approach. That is, first a linear controller is designed to show a desirable nominal performance by ignoring state constraints. Then, an additional compensator is introduced to account for state constraints. By minimizing a reasonable performance index, a dynamic compensator is derived explicitly, which is expressed in plant and controller parameters. The proposed method not only provides a graceful performance degradation, but it also guarantees the total stability of the resulting systems. An illustrative example is given to show the effectiveness of the proposed method.     

The constrained longest common subsequence problem

This paper considers a constrained version of longest common subsequence problem for two strings. Given strings S₁, S₂ and P, the constrained longest common subsequence problem for S₁ and S₂ with respect to P is to find a longest common subsequence lcs of S₁ and S₂ such that P is a subsequence of this lcs. An O(rn²m²) time algorithm based upon the dynamic programming technique is proposed for this new problem, where n, m and r are lengths of S₁, S₂ and P, respectively.     

园区网建设及有关技术分析

从系统工程方法出发，阐述园区网工程规划、设计、实施的一般性方法及各阶段目标和任务；分析了园区网建设中若干技术问题。     

分布式搜索引擎的设计与实现

在一个分布各地的网站群组成的大系统中，不设立中心数据库的情况下，各网站对等协调工作，实现数据库级共享与搜索是一个难题。文中阐述了用Web Service技术实现分布式搜索的基本原理，并对Web Service代理模式、异地数据存取、大结果集处理、查询数据本地化等关键技术进行了详细介绍。     

基于XML动态Web发布技术的实现

信息技术的发展使用户对Web服务的要求越来越多样化。而传统的动态Web发布技术难以满足这种变化，可扩展标记语言的出现无疑给这种变化带来新的发展契机。讨论了利用XML实现动态Web发布的基本原理，并通过实例说明了怎样利用XML中的文档对象模型和可扩展样式表单语言实现动态Web的发布。     

基于LabWindows/CVI的计算机图形动态模拟技术

计算机图形动态模拟是动态测试CAT系统的重要组成部分，本文提出了利用Labwindows/CVI实现动态模拟的基本原理与方法，并给出了拖拉机动态测试系统中仿真控制的实例，动态模拟功能设计成为相对独立的模块，有利于实现测试系统的自动化监控和操纵。     

Hierarchical Reliable Multicast: Performance Analysis and Optimal Placement of Proxies

This paper studies the use of multicast together with proxy nodes for reliably disseminating data from a single source to a large number of receivers. In order to achieve reliability, data must be retransmitted in case of loss either by the source or by special network nodes, called proxies. Each proxy is responsible for reliably delivering the data to a subgroup it is assigned. The multicast tree is partitioned into subgroups that form a hierarchy rooted at the source, hence the term hierarchical reliable multicast. The performance of this approach strongly depends on the topology and the loss characteristics of the underlying tree and the location of proxies. In the first part of the paper, we study the processing and bandwidth performance of such a reliable multicast dissemination given the tree and the placement of proxies. In the second part of the paper, we develop dynamic programming algorithms that give a placement of a fixed number of proxies on an arbitrary tree that minimizes the bandwidth used for reliable transfer. The first algorithm provides an optimal solution to the multicast proxies location problem in polynomial time, in the number of nodes and proxies. The second is an approximation algorithm that gives a solution with cost within a chosen precision from the optimal, in an improved running time. An optimal and an approximate solution are also provided for the proxies location problem if unicast is used for transmissions. Applications of this dynamic programming approach to related problems are discussed.