中间件技术的研究

计算机以及网络通信技术的发展使得中间件技术取得了长足的进步，出现了许多有关中间件的软件开发理论、标准协议以及各种商业软件产品。随着信息系统越来越以网络为中心进行开发和演化，中间件技术将扮演更加重要的角色。本文介绍了中间件领域的发展现状，主要分析了当前中间件领域中主流的DOC技术和正在兴起的Web Services、Grid／OGSA技术．并且我们根据未来分布式系统的多种需求，探讨了中间件领域将面临的挑战。     

An overview of the Real-Time CORBA specification

A growing class of real-time systems require end-to-end support for various quality-of-service (QoS) aspects, including bandwidth, latency, jitter and dependability. Applications include command and control, manufacturing process control, videoconferencing, large-scale distributed interactive simulation, and testbeam data acquisition. These systems require support for stringent QoS requirements. To meet this challenge, developers are turning to distributed object computing middleware, such as the Common Object Request Broker Architecture, an Object Management Group (OMG) industry standard. In complex real-time systems, DOC middleware resides between applications and the underlying operating systems, protocol stacks and hardware. CORBA helps decrease the cycle time and effort required to develop high-quality systems by composing applications using reusable software component services rather than building them entirely from scratch. The Real-Time CORBA specification includes features to manage CPU, network and memory resources. The authors describe the key Real-Time CORBA features that they feel are the most relevant to researchers and developers of distributed real-time and embedded systems     

A middleware architecture to facilitate distributed programming: DAROC: Data-Activated Replicated Object Communications

Programming distributed computer systems is difficult because of complexities in addressing remote entities, message handling, and program coupling. As systems grow, scalability becomes critical, as bottlenecks can serialize portions of the system. When these distributed system aspects are exposed to programmers, code size and complexity grow, as does the fragility of the system. This paper describes a distributed software architecture and middleware implementation that combines object-based blackboard-style communications with data-driven and periodic application scheduling to greatly simplify distributed programming while achieving scalable performance. Data-Activated Replication Object Communications (DAROC) allows programmers to treat shared objects as local variables while providing implicit communications.     

Software Architectures for Reducing Priority Inversion and Non-determinism in Real-time Object Request Brokers

There is increasing demand to extend Object RequestBroker (ORB) middleware to support distributed applications withstringent real-time requirements. However, conventional ORB implementations,such as CORBA ORBs, exhibit substantial priority inversion andnon-determinism, which makes them unsuitable for applicationswith deterministic real-time requirements. This paper providestwo contributions to the study and design of real-time ORB middleware.First, it illustrates empirically why conventional ORBs do notyet support real-time quality of service. Second, it evaluatesconnection and concurrency software architectures to identifystrategies that reduce priority inversion and non-determinismin real-time CORBA ORBs. The results presented in this paperdemonstrate the feasibility of using standard OO middleware likeCORBA to support certain types of real-time applications overthe Internet.     

A middleware‐transparent approach to developing distributed applications

An innovative middleware‐transparent approach to developing distributed applications is presented. The approach uses an aspect‐oriented software development technique to separate an application's middleware‐independent functionality from its middleware‐specific functionality. Application elements that are specific to the middleware are localized in aspects that can be seamlessly integrated into middleware‐independent application designs. The middleware‐transparent approach is used to decouple business functionality from middleware‐specific functionality. The decoupling allows developers to change middleware application elements without significantly modifying business functionality. Middleware technologies such as Java Remote Method Invocation (RMI), Jini, Simple Object Access Protocol (SOAP) remote procedure call (RPC) and .Net are used as examples to illustrate the approach. Copyright © 2005 John Wiley & Sons, Ltd.     

基于中间件的容错服务的研究

CORBA是一种当前流行的基于对象技术的中间件平台。它提供了一种松散的、异步的通信机制,解决分布式计算环境中不同硬件设备和软件系统的互联,增强了网络间软件的互操作性,解决传统分布式计算模式中的不足等问题。目前的CORBA产品大多缺乏容错机制,针对产品已有的缺陷和不足,给合了中间件技术的优点,运用对象复制技术和热备份技术实现容错服务。文章设计并实现了一种应用级容错CORBA系统,提高了系统的可靠性,满足了分布式系统对容错的要求。     

Comparative analysis of two different middleware approaches for reconfiguration of distributed real-time systems

Software-based reconfiguration of distributed real-time systems is a complex problem with many sides to it ranging from system-wide concerns down to the intrinsic non-robust nature of the specific middleware layer and the used programming techniques. In a completely open distributed system, mixing reconfiguration and real-time is not possible; the set of possible target states can be very large threatening the temporal predictability of the reconfiguration process. Over the last years, middle ware solutions have appeared mainly for general purpose systems where efficient state transitions are sought for, but real-time properties are not considered. One of the few contributions to run-time software reconfiguration in distributed real-time environments has been the iLAND middleware, where the germ of a solution with high potential has been conceived and delivered in practice.¹ The key idea has been the fact that a set of bounds and limitations to the structure of systems and to their open nature needs to be imposed in order to come up with practical solutions. In this paper, the authors present the different sides of the problem of software reconfiguration from two complementary middleware perspectives comparing two strategies built inside distribution middleware. We highlight the lessons learned in the iLAND project aimed at service-based reconfiguration and compare it to our experience in the development of distributed real-time Java reconfiguration based on distributed tasks rescheduling. Authors also provide a language view of both solutions. Lastly, empirical results are shown that validate these solutions and compare them on the basis of different programming language realizations.     

基于分布对象技术的移动中间件

基于JavaRMI技术的移动中间件存在一定程度的局限性。文中以中间件、分布对象计算和移动计算等相关领域的技术为背景,提出了基于分布对象技术的移动中间件MMDO(MobileMiddlewareBasedonDistributedObject),该体系结构包括:动态可定制的基础核心、通用移动Agent平台、异步消息服务、动态资源发现和移动用户安全注册。MMDO能够解决移动中间件研究存在的Java效率问题,同时拓展了移动服务,给移动应用提供更好的支撑环境。最后,给出仿真测试结果,证明了MMDO的有效性。     

反射式实时集成中间件

反射式实时集成中间件主要研究一类适应于分布式实时应用环境中软件合成与软件集成的构件粘合剂.这种中间件基于反射技术设计,用于分布式实时领域里实时构件间的粘合与集成,并能维护这些构件间交互协作环境的时间约束特征,保障环境变化的动态性和适应性以及降低协同工作环境中通讯机制的耦合度,实践软件复用思想在分布式实时应用领域中的应用.     

CORBA对象的复制技术研究

CORBA是一种当前流行的基于对象技术的中间件平台．CORBA对应用屏蔽了分布式系统的异构性．然而目前许多CORBA系统没有充分地考虑容错问题，而容错是运行在异构环境中的分布式应用的核心问题之一．因此，在最近几年对容错CORBA的研究成为CORBA技术的一个研究热点．本文讨论了对象复制技术的若干问题，提出了基于标准组通信机制的、能够容忍节点故障也能够容忍数值错误的基于选举的主动复制策略．     

实时CORBA规范分析与评述

实时系统是一类应用极为广泛的系统,而通用CORBA规范对实时应用支持不足,所以OMG制订了实时COR-BA1.0规范.。该规范支持固定优先级的实时CORBA应用,提供了实时CORBA应用中对象调用操作端到端的可预测性。文章对实时CORBA规范中所定义的控制和管理系统资源的策略和机制进行了较为详尽的阐述,并对其进行了分析与评述。     

An object infrastructure for Internet middleware. IBM on ComponentBroker

Middleware covers a variety of rapidly evolving capabilities. It began as software to fill the gaps as industry moved first to client-server and then to multi-tier distributed systems. As monolithic software was broken up and dispersed across servers, it became necessary to reconnect capabilities, manage disparate resources and functions, and access information and functions from remote requesters. This resulted in a host of software offerings for the middle tier. Component Broker is Internet middleware for distributed objects. It is designed to absorb complexity in the operational and development environment so that applications appear to be transparent, local and fully resourced. Component Broker is a complete package, with everything a developer needs to build, run and manage Web-enabled business objects, components and applications     

运载火箭测发控软件的中间件技术应用

由于不同型号硬件平台和软件平台的多样性,跨型号大规模融合应用系统通常要求在拥有多种软硬件平台(异构平台)的分布式环境下运行。借助中间件(Middleware)技术改进软件重用形式,提高软件重用程度,以实现支持分布式应用有效开发、部署、运行和管理的目的。本文在对现有火箭测发控系统软件的子系统功能聚类和程序架构分析基础上,开发基于中间件模型的通用火箭测发控系统软件。     

Generic support for distributed applications

In the late 1980s, software designers introduced middleware platforms to support distributed computing systems. Since then, the rapid evolution of technology has caused an explosion of distributed-processing requirements. Application developers now routinely expect to support multimedia systems and mobile users and computers. Timely response to asynchronous events is crucial to such applications, but current platforms do not adequately meet this need. Another need of existing and emerging applications is the secure interoperability of independent services in large-scale, widely distributed systems. Information systems serving organizations such as universities, hospitals, and government agencies require cross-domain interaction. To meet the needs of these applications, Cambridge University researchers developed middleware extensions that provide a flexible, scalable approach to distributed-application development. This article details the extensions they developed, explaining their distributed software approach and the support it has provided for emerging applications     

容错CORBA系统的设计与实现

CORBA是基于对象技术的中间件平台的最流行的标准之一 .CORBA对应用屏蔽了分布式系统的异构性 .然而目前 CORBA还没有考虑容错问题 ,而容错是运行在异构环境中的分布式应用的核心问题之一 .因此 ,在最近几年许多为 CORBA应用添加可靠性和可用性的建议出现在各种文献上 .本文分析了这些建议的优、缺点 ,并提出了一个新颖的与 CORBA兼容的方法 ,这种方法不同于异步环境中可靠结构的分发方法 .     

A new fuzzy-decision based load balancing system for distributed object computing

Distributed object computing systems are widely envisioned to be the desired distributed software development paradigm due to the higher modularity and the capability of handling machine and operating system heterogeneity. Indeed, enabled by the tremendous advancements in processor and networking technologies, complex operations such as object serialization and data marshaling have become very efficient, and thus, distributed object systems are being built for many different applications. However, as the system scales up (e.g., with larger number of server and client objects, and more machines), a judicious load balancing system is required to efficiently distribute the workload (e.g., the queries, messages/objects passing) among the different servers in the system. Unfortunately, in existing distributed object middleware systems, such a load balancing facility does not exist. In this paper, we present the design and implementation of a new dynamic fuzzy-decision-based load balancing system incorporated in a distributed object computing environment. Our proposed approach works by using a fuzzy logic controller which informs a client object to use the most appropriate service such that load balancing among servers is achieved. We have chosen Jini to build our experimental middleware platform, on which our proposed approach as well as other related techniques are implemented and compared. Extensive experiments are conducted to investigate the effectiveness of our fuzzy-decision-based algorithm, which is found to be consistently better than other approaches.     

基于中间件的角色访问控制

基于角色的访问控制RBAC技术是随着计算机信息系统的迅速发展而发展起来的。在RBAC中,角色是其核心概念,它根据用户在组织内所处的角色进行访问授权与控制,通过角色沟通用户与控制对象。另一方面,CORBA由于分布式异构环境的存在而成为中间件的公认标准。本文尝试将两种主流技术进行有机结合来实现安全访问控制的技术。     

Middleware infrastructure for parallel and distributed programming models in heterogeneous systems

We introduce a middleware infrastructure that provides software services for developing and deploying high-performance parallel programming models and distributed applications on clusters and networked heterogeneous systems. This middleware infrastructure utilizes distributed agents residing on the participating machines and communicating with one another to perform the required functions. An intensive study of the parallel programming models in Java has helped identify the common requirements for a runtime support environment, which we used to define the middleware functionality. A Java-based prototype, based on this architecture, has been developed along with a Java object-passing interface (JOPI) class library. Since this system is written completely in Java, it is portable and allows executing programs in parallel across multiple heterogeneous platforms. With the middleware infrastructure, users need not deal with the mechanisms of deploying and loading user classes on the heterogeneous system. Moreover, details of scheduling, controlling, monitoring, and executing user jobs are hidden, while the management of system resources is made transparent to the user. Such uniform services are essential for facilitating the development and deployment of scalable high-performance Java applications on clusters and heterogeneous systems. An initial deployment of a parallel Java programming model over a heterogeneous, distributed system shows good performance results. In addition, a framework for the agents' startup mechanism and organization is introduced to provide scalable deployment and communication among the agents.     

浅析中间件技术的研究现状

中间件是为解决分布式环境中的异构问题而提出的,它是当前软件技术发展的一个潮流,是发展最快的软件品种之一。该文阐述了中间件技术的概念、分类、优势以及作用,同时提出了目前中间件的发展趋势。     

Evolutionary multi-objective optimization of QoS-Aware Publish/Subscribe Middleware in electronics production

Computer-Aided Manufacturing using XML (CAMX) production systems are built on Message-Oriented Middleware Frameworks, offering standards-based communication among machines and control software applications. CAMX Frameworks implement Publish/Subscribe of XML messages through an entity called the Message Broker (MSB), which provides the messaging service using a Simple Object Access Protocol (SOAP) interface. In order to create scalable frameworks, distributed MSB systems are deployed. However, the topology optimization problem arises, as clients need to be assigned to one of many MSB nodes. The problem is strictly NP-hard, and multiple optimization criteria are conflicting. A solution considering real-time systems was developed based on Evolutionary Multi-Objective Optimization techniques. The Framework Optimization Algorithm (FOA) is designed to work with various topologies, including federated frameworks, locally distributed clusters, and mixed environments including embedded middleware nodes. The developed FOA was tested for a case scenario based on a flexible manufacturing system running on a distributed CAMX framework, and proved to robustly converge to the optimal topology. Convergence was achieved within few seconds, demonstrating the suitability of FOA for rapid topology reconfiguration in response to changes in the system.