UML动态建模方法在DDSS模型访问中的应用

统一建模语言(unified modeling language,UML)是面向对象软件开发方法的重要技术.决策支持系统中的模型库管理对于整体决策支持系统来说尤其重要,在分布式环境下,如何实现模型库中模型的查询、修改、增加和删除对于整体系统的性能起到决定作用,使用UML的动态建模技术,设计并实现了基于C/S模式下的DSS模型库管理系统的模型访问,并描述了通过UML来进行动态建模的详细过程.     

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.     

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。     

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     

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.     

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.     

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     

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。     

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.     

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     

Advanced data processing in KRISYS: modeling concepts, implementation techniques, and client/server issues

The increasing power of modern computers is steadily opening up new application domains for advanced data processing such as engineering and knowledge-based applications. To meet their requirements, concepts for advanced data management have been investigated during the last decade, especially in the field of object orientation. Over the last couple of years, the database group at the University of Kaiserslautern has been developing such an advanced database system, the KRISYS prototype. In this article, we report on the results and experiences obtained in the course of this project. The primary objective for the first version of KRISYS was to provide semantic features, such as an expressive data model, a set-oriented query language, deductive as well as active capabilities. The first KRISYS prototype became completely operational in 1989. To evaluate its features and to stabilize its functionality, we started to develop several applications with the system. These experiences marked the starting point for an overall redesign of KRISYS. Major goals were to tune KRISYS and its query-processing facilities to a suitable client/server environment, as well as to provide elaborate mechanisms for consistency control comprising semantic integrity constraints, multi-user synchronization, and failure recovery. The essential aspects of the resulting client/server architecture are embodied by the client-side data management needed to effectively support advanced applications and to gain the required system performance for interactive work. The project stages of KRISYS properly reflect the essential developments that have taken place in the research on advanced database systems over the last years. Hence, the subsequent discussions will bring up a number of important aspects with regard to advanced data processing that are of significant general importance, as well as of general applicability to database systems. Received June 18, 1996 / Accepted November 11, 1997     

A data/knowledge paradigm for the modeling and design of operationssupport systems

The paper develops the Smart Object paradigm and its instantiation, which provide a new conceptualization for the modeling, design, and development of an important but little researched class of information systems, operations support systems (OSS). OSS is the authors' term for systems which provide interactive support for the management of large, complex operations environments, such as manufacturing plants, military operations, and large power generation facilities. The most salient feature of an OSS is its dynamic nature. The number and kind of elements composing the system as well as the mode of control of those elements change frequently in response to the environment. The abstraction of control and the ease with which complex dynamic control behavior can be modeled and simulated is one of the important aspects of the paradigm. The framework for the Smart Object paradigm is the fusion of object-oriented design models with declarative knowledge representation and active inferencing from AI models. Additional defining concepts from data/knowledge models, semantic data models, active databases, and frame based systems, are added to the synthesis as justified by their contribution to the ability to naturally model OSS at a high level of abstraction. The model assists in declaratively representing domain data/knowledge and its structure, and task or process knowledge, in addition to modeling multilevel control and interobject coordination     

A group Undo/Redo method in 3D collaborative modeling systems with performance evaluation

Undo/Redo is an indispensable function in 3D collaborative modeling systems where a single mistake conducted by one user is propagated to all participants. Both intention preservation and consistency maintenance should be satisfied when applying group Undo/Redo. Besides, fast local responsiveness and timely group awareness are accepted performance metrics in interactive systems. In this paper, we contribute a novel group Undo/Redo mechanism for 3D collaborative modeling systems to support the “any time, any where” Undo/Redo. Response time will be shortened noticeably with a Model State Stream kept on each collaborative site. In the case of concurrent Undo/Redo, an Undo State Vector is proposed to ensure the Undo/Redo intention preservation and model consistency maintenance. Furthermore, the paper studies the performance of the algorithm including the worst, best and average cases with theoretical analyses. Our experiments show that responsive time is actually depending on a number of factors such as size of the history buffer, execution time for a single modeling operation.     

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.     

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。