Reversible client/server interactions

In the setting of session behaviours, we study an extension of the concept of compliance when a disciplined form of backtracking and of output skipping is present. After adding checkpoints to the syntax of session behaviours, we formalise the operational semantics via an LTS, and define natural notions of checkpoint compliance and sub-behaviour, which we prove to be both decidable. Then we extend the operational semantics with skips and we show the decidability of the obtained compliance.     

客户机／服务器系统测试

针对客户机／服务器系统的特点,运用软件工程的方法,以《国家图书馆典藏流通系统》的测试做为例子,论述了客户机／服务器系统测试的几个值得注意的方面。     

基于口令的客户端/服务器认证协议

身份认证是建立客户端和服务器之间安全会话的前提条件。Kim和Chung提出了一种双方的双向认证方案,其以较小的计算量得到了学者们的关注。但经分析发现,该方案并不安全：无法抵抗离线口令猜测攻击和无限次在线口令猜测攻击,也不能防止服务器伪装攻击。为了解决这些安全隐患,利用非对称Rabin密码体制提出了一种改进的方案,并基于BAN逻辑对方案的正确性进行了严格验证。最后还分析了新方案的安全性和性能。     

Distributed coordination models for client/server computing

A major limitation in the basic client/server model is its focus on clients requesting individual services. Clients often need to invoke multiple services, coordinated to reflect how those services interrelate and contribute to the overall application. Important examples include task allocation and event notification in collaborative workgroup systems, and task sequencing and routing in workflow applications. Failure to address control requirements for such interactions has impeded development of uniform methods and tools for building many types of distributed systems with client/server architectures. The article identifies and examines extensions to the basic client/server model that provide explicit support for coordinating multiserver interactions     

Where is client/server software headed?

Computers have moved to desktops; now, the underlying software is itself evolving. The direction computing will take is clear, but the route it will take is a matter for some speculation. We examine several promising software ideas, especially distributed software and its underlying infrastructure called middleware. Industrial software is being driven by document-centric design, reusable component implementation based on industry standards, and end-user programming     

Technology for testing nondeterministic client/server database applications

The execution of a client/server application involving database access requires a sequence of database transaction events (or, T-events), called a transaction sequence (or, T-sequence). A client/server database application may have nondeterministic behavior in that multiple executions thereof with the same input may produce different T-sequences. We present a framework for testing all possible T-sequences of a client/server database application. We first show how to define a T-sequence in order to provide sufficient information to detect race conditions between T-events. Second, we design algorithms to change the outcomes of race conditions in order to derive race variants, which are prefixes of other T-sequences. Third, we develop a prefix-based replay technique for race variants derived from T-sequences. We prove that our framework can derive all the possible T-sequences in cases where every execution of the application terminates. A formal proof and an analysis of the proposed framework are given. We describe a prototype implementation of the framework and present experimental results obtained from it.     

When client/server isn't enough: coordinating multiple distributedtasks

Computing in a distributed environment for multitasked cooperative work is a promising area that presents many coordination issues. Our prototype system implements a three-layer architecture to provide greater control and flexibility in the distributed multitasking environment. The architecture includes a groupware server, application servers, and clients. The architecture can be further refined to provide more flexible control of activities. More applications, such as group calendaring and participative design can also be studied to find their idiosyncratic coordination needs and to elaborate the division of labor among different servers and clients     

A dynamic binary translation system in a client/server environment

With rapid advances in mobile computing, multi-core processors and expanded memory resources are being made available in new mobile devices. This trend will allow a wider range of existing applications to be migrated to mobile devices, for example, running desktop applications in IA-32 (x86) binaries on ARM-based mobile devices transparently using dynamic binary translation (DBT). However, the overall performance could significantly affect the energy consumption of the mobile devices because it is directly linked to the number of instructions executed and the overall execution time of the translated code. Hence, even though the capability of today’s mobile devices will continue to grow, the concern over translation efficiency and energy consumption will put more constraints on a DBT for mobile devices, in particular, for thin mobile clients than that for severs. With increasing network accessibility and bandwidth in various environments, it makes many network servers highly accessible to thin mobile clients. Those network servers are usually equipped with a substantial amount of resources. This provides an opportunity for DBT on thin clients to leverage such powerful servers. However, designing such a DBT for a client/server environment requires many critical considerations.In this work, we looked at those design issues and developed a distributed DBT system based on a client/server model. It consists of two dynamic binary translators. An aggressive dynamic binary translator/optimizer on the server to service the translation/optimization requests from thin clients, and a thin DBT on each thin client to perform lightweight binary translation and basic emulation functions for its own. With such a two-translator client/server approach, we successfully off-load the DBT overhead of the thin client to the server and achieve a significant performance improvement over the non-client/server model. Experimental results show that the DBT of the client/server model could achieve 37% and 17% improvement over that of non-client/server model for x86/32-to-ARM emulation using MiBench and SPEC CINT2006 benchmarks with test inputs, respectively, and 84% improvement using SPLASH-2 benchmarks running two emulation threads.     

基于Client/Server数据完整性约束的实现技术

主要讨论基于Client/Server数据完整性约束及其如何实施了企业业务规则，并以SQLServer和PowerBuilder5．0为例，介绍了数据完整性约束的实现技术。     

基于Agent的客户机/服务器模型的设计与实现

在对Agent技术、多Agent技术以及Client/Agent/Server（客户机/代理/服务器）模式的理论分析基础上,指出了传统C/S结构的不足,提出了基于Agent的两层Agent/Server模式.然后基于该模式,给出了一个Agent/Server框架,简称ASFtame.由于引入了先进的FIPA标准和多Agent开发思想,ASFrame能充分发挥移动Agent的移动性,从而提高了应用系统的伸缩性和智能性.     

A flexible and recoverable client/server database event notification system

A software architecture is presented that allows client application programs to interact with a DBMS server in a flexible and powerful way, using either direct, volatile messages, or messages sent via recoverable queues. Normal requests from clients to the server and replies from the server to clients can be transmitted using direct or recoverable messages. In addition, an application event notification mechanism is provided, whereby client applications running anywhere on the network can register for events, and when those events are raised, the clients are notified. A novel parameter passing mechanism allows a set of tuples to be included in an event notification. The event mechanism is particularly useful in an active DBMS, where events can be raised by triggers to signal running application programs. Received July 21, 1995 / Accepted May 30, 1996     

Middleware: any client, any server

The Internet and enterprise intranets are all about middleware. Middleware is the center of the client/server architecture. All major vendors focus on it. After all, “occupy the center” is a good chess strategy. However, unlike chess, the Internet develops as a multi-player game, and occupying the center is a collaborative exercise in which the winners are determined by the Internet's ubiquity. CICS (Customer Information Control System) is an IBM transaction monitor that IBM has made into a suite of middleware products which neatly illustrate the condensation process whereby common application functionality “condenses” into middleware. Very briefly, CICS today addresses the problem of managing an Internet site being hit by thousands of HTML form requests     

客户机/服务器模式中传输层协议的比较与选择

传输层协议的选择影响着带宽利用率、响应时间等重要的网络性能指标。本文分析比较了三种标准的传输层协议,提出了T/TCP可能是未来的主要趋势。     

A method for design and performance modeling of client/server systems

Designing complex distributed client/server applications that meet performance requirements may prove extremely difficult in practice if software developers are not willing or do not have the time to help software performance analysts. The paper advocates the need to integrate both design and performance modeling activities so that one can help the other. We present a method developed and used by the authors in the design of a fairly large and complex client/server application. The method is based on a software performance engineering language developed by one of the authors. Use cases were developed and mapped to a performance modeling specification using the language. A compiler for the language generates an analytic performance model for the system. Service demand parameters at servers, storage boxes, and networks are derived by the compiler from the system specification. A detailed model of DBMS query optimizers allows the compiler to estimate the number of I/Os and CPU time for SQL statements. The paper concludes with some results of the application that prompted the development of the method and language.     

三层C/S结构的金属蠕变虚拟试验系统

一般金属蠕变试验有温度高、周期长的局限,运用JBuilder、JAVA 3D、VRML和3DS MAX等为主要开发工具,设计开发金属蠕变虚拟试验系统.该系统基于三层C/S结构,主要由三维试验场景与GUI用户界面组成的客户端、应用服务层以及后台数据库服务器管理程序组成.具有虚拟场景形象逼真、动态组合、实时保存和虚拟实验的交互性强、操作简便、动态扩充等特点,为理工科学生和一般工程技术人员学习、研究和应用蠕变试验,提供了快速高效的辅助工具.     

基于客户/服务器模式的远程控制系统

随着计算机和远程通讯为代表的信息技术的飞速发展和广泛应用,使远程监控、远程教育、远程贸易和服务成为可能。提出了一种基于客户／服务器模式的交流伺服控制器的远程监控系统,阐述了其体系结构及各部分功能,并开发了基于TCP／IP协议的远程通信实用程序。