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.     

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。     

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.     

Predicting client/server availability

Client/server availability is a complex issue due to the many possible configurations of client/server environments and failure modes of client, server, and network devices. Such complexity makes it difficult to properly account for availability in client/server architectural design. I present a methodology and data to help design engineers evaluate client/server availability. I evaluate client/server outage data, indicate the most important outage causes in a client/server environment, and discuss methods for improving client/server availability     

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.     

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。     

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。     

基于客户/服务器模式的电力系统管理及故障诊断专家系统的开发

介绍一种基于客户／服务器的电子系统管理及故障诊断专家系统。该系统以Ｗｉｎ－ｄｏｗｓＮＴ为平台，采用客户／服务器网络结构，在服务器端由数据库服务器——ＳＱＬＳｅｒｖｅｒ统一管理数据库，并利用开放的数据库连接（ＯＤＢＣ）和ＶｉｓｕａｌＦｏｘＰｒｏ３．０开发客户端应用程序。     

基于C/S结构的车辆监控系统设计与实现

介绍了一个基于客户／服务器模式的车辆监控系统的设计原理和系统的数据传送过程,分析了服务器端和客户端的工作流程,阐述了在VC编程环境下如何利用Socket编程机制实现总控中心和各分控中心的数据交换,以及如何利用ADO数据访问技术实现监控平台与数据库服务器的数据交互,并给出了实例说明。     

On developing an inventory management system in the client/server environment

It is reported that client/server technology can make it easier for users to access information, to use and to develop applications, and to manage a distributed computing environment. This paper describes the implementation of client/server technology to an inventory management system. Methodology developed and barriers faced in this study are useful for practitioners in building client/server applications.     

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.     

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.     

A Mechanism Supporting the Client/Server Relationship in the Operating System of Distributed System “THUDS”

This paper presents a distributed operating system modeled as an abstract machine that provides all the distributed processes with the same set of services.The kernel of our operating system supports services which are achieved by a remote procedure call on requests by parallel processes.Therefore,a scheme for solving the client-server relationship is required.In our system there are more than one clients and,at least,a receive would be required for each.Similarly,there are more than one servers such that the send in a client should produce a message that can be received by every server.Consequently,a mechanism well suited for programming multiple-clients/single-server and single-client/multiple-servers interactions is proposed.     

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     

分布式数据库服务器的可信性研究

主要介绍了分布式数据库服务器系统中的可信研究,并讨论了其中有关可信授权的实现、权限的管理逻辑以及授权机的具体运行过程,给出了可信分布式数据库服务器系统的模型。系统中采用了信任链机制、基于角色的访问控制模型、两级日志、可信认证等技术,同时给出了可信在分布式计算机系统中的实现技术和途径。     

A trusted decentralized access control framework for the client/server architecture

This paper proposes a trusted decentralized access control (TDAC) framework for the client/server architecture. As the fundamental principle, TDAC enforces access control policies at the client side and protects sensitive objects at the server side by leveraging trusted computing technologies. Compared with the previous work of Sandhu and Zhang (2005), TDAC uses fewer requirements for trusted components. To implement TDAC, we design a private trusted reference monitor that runs at the client side, evaluates an access control request, and signs a temporary access control credential for a client application trustworthily; we also design a master reference monitor that runs at the server side, evaluates the request from the client application only according to the temporary access control credential. As a typical application, TDAC can protect client's private context data in subject-context aware access control.     

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.