CORBA:全面的分布式对象计算(下)

文章是［１］的续篇,讨论ＯＲＢ和对象适配器（Ｏｂｊｅｃｔ　Ａｄａｐｔｅｒ）对服务对象的管理,及ＯＲＢｓ间的互操作性问题。并指出ＣＯＲＢＡ和ＪａｖａＢｅａｎｓ结合的趋势,最后比较ＣＯＲＢＡ与ＲＭＩ、ＤＣＯＭ的性能。     

CORBA,DCOM和Java/RMI技术比较

分布式对象技术主要是在分布式异构环境下建立应用系统框架和对象构件,在应用系统框架的支撑下,开发者可以将软件功能包装为更易管理和使用的对象,这些分布式对象可以跨越不同的软硬件平台进行互操作。现在比较流行的三种重要的分布对象技术,它们是OMG的公对象请求代理体系结构(CORBA),Microsoft的分布式组件对象模型(DCOM),以及JavaSoft的Java/远程方法调用(Java/RMI)。本文将从编程人员以及架构师的角度,分析比较这三种分布对象技术之间的区别以及它们各自的优缺点。     

Integrating Java and CORBA: a programmer's perspective

The introduction of Java's proprietary remote method invocation (RMI) with version 1.1 of the Java Development Kit simplified the challenging task of developing distributed object-based systems. RMI provides convenient integration with Java; however, it lacks interoperability with other languages. The Object Management Group's Common Object Request Broker Architecture (CORBA), on the other hand, is a platform- and language-neutral specification for developing distributed object systems. CORBA provides services not covered by RMI, such as managing transactional safety and persistency. We use a small chat room application to describe how a programmer can combine Java RMI's ease of use with CORBA's language neutrality. We start with an implementation based on a set of distributed objects using RMI. We then adapt the example to CORBA or, more specifically, the RMI-over-IIOP (Internet inter-ORB protocol) specification developed by Sun and IBM     

Applications of dynamic proxies in distributed environments

In object‐oriented programming (OOP), proxies are entities that act as an intermediary between client objects and target objects. Dynamic proxies can be used to construct distributed systems that support the open implementation approach and promote code reuse. The OO paradigm supports code reuse through various ways including inheritance, polymorphism and aggregation. In this paper, we adopt a definition of software reuse restricted to reuse of code components and address the question of constructing distributed systems based on dynamic proxies. Different networking techniques and programming paradigms such as Java's Remote Method Invocation (RMI), the Common Object Request Broker Architecture (CORBA) and Java Servlets are used to implement the distributed client/server architecture. Copyright © 2004 John Wiley & Sons, Ltd.     

基于SOA架构的实时通讯机制在电力行业计量自动化系统中的应用

电力行业的计量自动化系统,是以SOA架构模式的应用系统,随着应用需求复杂度的提高以及实时应用能力要求的不断提升．传统DCOM、CORBA、RMI等中间件技术逐渐显露出它的弊端。SUN公司推出的JMS技术规范是一种面向消息的中间件MOM．它能够很好的解决电力计量自动化系统的实时通讯问题。该文阐述了一种传统的后台实时架构模式＋SOA架构模式来设计电力计量自动化系统．在技术架构和应用上都能够满足现有需求。     

AGORA: a search engine for software components

Using JavaBeans and CORBA agents in conjunction with Web search technologies, this prototype search engine (Agora), automatically generates and indexes a worldwide database of software products, classified by component model. Users of Agora can search for components in this database by describing specific properties of a component's interface. The system combines Web search engines with an introspection process. Introspection, primarily associated with JavaBeans, describes the capability of components to provide information about their own interfaces. The Common Object Request Broker Architecture offers a similar capability, although this data is maintained external to the CORBA server in an interface repository     

反射中间件的研究

中间件处理的是复杂的分布式应用问题，因而常常面对变化的运行环境和不同的用户需求。当前的中间件，无论CORBA、DCOM还是JavaRMI基本上都采用了黑箱抽象的原则，缺少必要的灵活性和适应性。通过反射技术，可以使客户检索和调整系统的内部实现，以满足客户的特定服务质量要求。通过比较中间件的工作过程与反射计算，文章提出采用绑定具体化反射模型来设计中间件，并分析了这个反射模型的特点。文章还从绑定生成器、反射协议模栈，可配置的反射层等方面，介绍了一个反射中间件原型RECOM的实现。     

MICO: an open source CORBA implementation

The Common Object Request Broker Architecture is a specification for creating, distributing, and managing distributed program objects across a network. Both the International Organization for Standardization and X/Open have sanctioned CORBA as the standard middleware architecture for distributed objects. CORBA was specifically designed to support heterogeneous environments, different vendors' products, and several popular programming languages. MICO is an OSS implementation of CORBA. Inspired by the GNU project, the name "MICO" stands for "MICO Is CORBA". MICO has evolved into a mature open source project, with close to a half million lines of source code contributed by more than 150 programmers. The author discusses MICO's internal architecture and then offers a few guidelines to choose the right CORBA implementation for your purposes.     

基于XML的分布式计算

由于数据格式不兼容，分布式计算模型DCOM，CORBA和RMI之间的交互非常困难，XML协议作为一个通用的数据描述方式为分布式计算提供了新的思路。提出了一种基于XML的分布式对象代理的实现方法，并详细分析了数据与RPC的编组实现过程，在这种方法的支持下，分布式计算方便地跨越了不同的操作系统与编程环境，极大地提高了兼容性和互操作性，同时，由于XML的开放性，这种方法也具有很好的扩展性。     

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.     

CORBA vs DCOM 实现分布式应用

CORBA(Common Object Request Broker Architecture)和DCOM(Distributed Component Object Model)是现在最流行的两种分布式对象模型，通过在NFS-XDII(Net Finance Systemxidian version2．0)系统中的开发，阐述了CORBA和DCOM实现分布式应用的原理和结构，对比了CORBA和DCOM的特点。     

MobiPADS: a reflective middleware for context-aware mobile computing

Traditionally, middleware technologies, such as CORBA, Java RMI, and Microsoft's DCOM, have provided a set of distributed computing services that essentially abstract the underlying network services to a monolithic "black box." In a mobile operating environment, the fundamental assumption of middleware abstracting a unified distributed service for all types of applications operating over a static network infrastructure is no longer valid. In particular, mobile applications are not able to leverage the benefits of adaptive computing to optimize its computation based on current contextual situations. In this paper, we introduce the Mobile Platform for Actively Deployable Service (MobiPADS) system. MobiPADS is designed to support context-aware processing by providing an executing platform to enable active service deployment and reconfiguration of the service composition in response to environments of varying contexts. Unlike most mobile middleware, MobiPADS supports dynamic adaptation at both the middleware and application layers to provide flexible configuration of resources to optimize the operations of mobile applications. Within the MobiPADS system, services (known as mobilets) are configured as chained service objects to provide augmented services to the underlying mobile applications so as to alleviate the adverse conditions of a wireless environment.     

异种分布式对象技术互操作的分析与设计

现在以CORBA，DCOM和RMI为代表的三种分布式对象技术日益流行和不断发展，然而对于它们的互操作是否可行？主要就这三种技术在传统模式和基于Web的模式两种环境下对于它们的桥接和互操作进行一些研究和分析。     

支持QoS的IIOP的设计和实现

随着网络技术和中间件技术的发展,许多分布式应用（如多媒体,实时应用）要求支持多种QoS,如端到端的延迟、丢失率等。QoS与中间件平台的集成自然成了人们研究的焦点。当前流行的面向对象的中间件,如CORBA,DCOM和Java/RM1,在这一方面还不成熟。GIOP／IIOP是异种ORB在TCP／IP网络上互操作的基础,因而支持QoS的IIOP是支持QoS的CORBA的基础。本文首先简要介绍了IP的QoS模型和Windows2000中的QoS技术。在此基础上,详细讨论了支持了QoS的IIOP的设计和实现。     

面向服务的C2系统集成实现方式比较

分别简要概括了目前指控系统集成中主流的SOA实现方式,从实现方法、互操作性和服务质量等方面比较了CORBA、DCOM、RMI、Jini以及DDS实现方式在指控系统集成中的特点.分析了指控系统服务化实现的特点和需求,指出了当前各种实现方式在指控系统服务化集成中的优劣.提出了一种适用于分布式实时大容量数据交互环境下集成方式.     

The use of adapters to support interoperability of components for reusability

Interoperability of heterogeneous applications is defined as the ability for multiple software applications written in different programming languages running on different platforms with different operating systems to communicate and interact with one another over different computer networks. The emerging middleware technologies, including CORBA, COM/DCOM, and Enterprise JavaBeans offer an industrial defacto standard communication infrastructure to support the interoperability of heterogeneous applications in components. However, the implementation of a component suffers from high interaction complexities in the component that seriously degrades the application independence. Software components should be built to be independent of the context in which they are used, allowing them to be reused in many different computing environments. In this paper, we are presenting an adapter to isolate, encapsulate, and manage a component's interactions outside the component. The dynamic interface binding was designed to allow an adapter to examine the signature of the requested services at runtime such as operation names, parameters orders, parameters types, and parameters sizes. The interfaces of interconnecting components are bound at runtime. In addition, the interface language mapping allows an interface in a specific programming language to be automatically generated from an IDL interface. The use of adapters increases the reusability of components and also simplifies the integration of the components to an application.     

三种主流中间件之比较

中间件本质是对分布式应用的抽象，其运用范围越来越广，目前流行的主要有三种：OMG组织的CORBA，Microsoft公司的COM／DCOM和SUN公司的JavaRMI。首先简要介绍了这三种中间件技术，然后在体系结构，对象服务，跨平台和语言支持能力、性能等方面分析对比了它们的特点，最后，讨论了它们各自的应用范围和发展趋势。     

分布式系统中对象获取方法的研究

1 引言 DCOM是微软公司提出的一种分布式组件对象模型(Distributed Component Object Model)。DCOM起源于动态数据交换(DDE)技术,实现应用程序之间共享数据的动态交换,对象连接与嵌入OLE就是从DDE引伸而来。随后引入的组件对象模型(Component Object Model),形成了对象之间实现互操作的二进制标准。DCOM是COM在分布计算方面的自然延续,它为分布在网络不同节点的COM构件提供了互操作的基础结构。     

DCOM技术在ICAS中的应用

根据ICAS系统需求的具体情况，通过对三种部件技术的优缺点以及适应性分析，选取DCOM作为ICAS系统的核心开发技术，并在此基础上设计出了ICAS系统的结构图及开发策略。