Java based replicated server objects and their remote method invocations in a distributed environment

A distributed system is said to be fault‐tolerant if it is able to provide important services despite partial failures of the computers or software objects in the system. These systems are needed to support applications such as remote access and control, virtual mobile offices and wide area collaborative systems where there are chances of failures in the network and software objects. Fault‐tolerance is usually achieved by replicating the objects in the system. Traditional distributed applications constructed using Java RMI (remote method invocation) are not fault‐tolerant because of the lack of support of object replication. The objective of the present work is to design a remote method invocation that supports server object replication. To provide a fault‐tolerant service to the remote client objects, server objects are actively replicated. The problems associated with the method invocation in the context of active server object replication are presented and solutions are discussed and implemented. Copyright © 2001 John Wiley & Sons, Ltd.     

基于Web Service的一种分布式体系结构

基于Web Service的框架为电子商务提出了一种新的分布式体系结构，它可以跨越应用系统的对象体系、运行平台、开发语言等的界限，以服务的形式封装应用并对外发布，供用户或其它企业调用，从而形成一个其于Web的服务共享平台。从WebService的概念入手，详细介绍了Web Service框架的标准、组件结构及其发展动态，并对现有的产品进行了比较。     

PROM:A Support for Robust Replication in a Distributed Object Environment

The concept of object can be employed to achieve tolerance to hardware faults in distributed systems.Replication by introducing several copies for each object allows a continuous service even in case of failure.In particular,the paper describes an object model,PROM,which exploits replication by defining several passive back-up copies for any object.The system automatically reovers any failure of a copy in execution by activating a spare copy and restarting it from a previous checkpoint.The aim of the paper is the analysis of the effective support for PROM.This support is organized in structured levels on a distributed architecture.The services that the support should include to guarantee the desired replication model are described.     

Replication Management in Reliable Real-Time Systems

Building reliable real-time applications on top of commercial off-the-shelf (COTS) components is not a straightforward task. Thus, it is essential to provide a simple and transparent programming model, in order to abstract programmers from the low-level implementation details of distribution and replication. However, the recent trend for incorporating pre-emptive multitasking applications in reliable real-time systems inherently increases its complexity. It is therefore important to provide a transparent programming model, enabling pre-emptive multitasking applications to be implemented without resorting to simultaneously dealing with both system requirements and distribution and replication issues. The distributed embedded architecture using COTS components (DEAR-COTS) architecture has been previously proposed as an architecture to support real-time and reliable distributed computer-controlled systems (DCCS) using COTS components. Within the DEAR-COTS architecture, the hard real-time subsystem provides a framework for the development of reliable real-time applications, which are the core of DCCS applications. This paper presents the proposed framework, and demonstrates how it can be used to support the transparent replication of software components.     

Replication techniques for speeding up parallel applications on distributed systems

Most methods for programming loosely coupled systems are based on message-passing. Recently, however, methods have emerged based on ‘virtually’ sharing data. These methods simplify distributed programming, but are hard to implement efficiently, as loosely coupled systems do not contain physical shared memory. We introduce a new model, the shared data-object model, that eases the implementation of parallel applications on loosely coupled systems, but can still be implemented efficiently. In our model, shared data are encapsulated in passive data-objects, which are variables of user-defined abstract data types. To speed up access to shared data, data-objects are replicated. This ability to replicate objects is a significant difference with other object-based models (e.g. Emerald and Amber). Also, by replicating logical objects rather than physical pages, our model has many advantages over shared virtual memory systems. This paper discusses the design choices involved in replicating objects and their effect on performance. Important issues are: how to maintain consistency among different copies of an object; how to implement changes to objects; which strategy for object replication to use. We have implemented several options to determine which ones are the most efficient.     

Symmetric active/active metadata service for high availability parallel file systems

High availability data storage systems are critical for many applications as research and business become more data driven. Since metadata management is essential to system availability, multiple metadata services are used to improve the availability of distributed storage systems. Past research has focused on the active/standby model, where each active service has at least one redundant idle backup. However, interruption of service and even some loss of service state may occur during a fail-over depending on the replication technique used. In addition, the replication overhead for multiple metadata services can be very high. The research in this paper targets the symmetric active/active replication model, which uses multiple redundant service nodes running in virtual synchrony. In this model, service node failures do not cause a fail-over to a backup and there is no disruption of service or loss of service state. A fast delivery protocol is further discussed to reduce the latency of the total order broadcast needed. The prototype implementation shows that metadata service high availability can be achieved with an acceptable performance trade-off using the symmetric active/active metadata service solution.     

Improving Resource Management in Distributed Systems using Language-Level Structuring Concepts

Currently, a shift of paradigm from sequential to distributed computing can be observed. Tremendous efforts are needed to cope with the challenging demands that are inherent to this transition. The two most important issues concern programming support for developing large-scale distributed applications and the efficient execution of such applications on top of a distributed hardware configuration. This paper presents a new language and object-based approach called MoDiS to cope with these demands. Distributed systems are developed and transformed into executables following a systematic, top-down driven method. Language-level is intended to mean that a high-level programming language is used to develop operating system services as well as user-level applications. The language-level concepts employed are based on objects and support advanced structuring features. Structural dependencies between objects are implicitly determined at the application level and exploited by the distributed resource management system to transform applications into efficient executables.     

XML Web Services在电子办公中的应用

该文介绍了电子办公系统的发展现状以及存在的问题,提出了一种新的、分布式、基于XMLWebServices的电子办公系统的体系结构,它可以跨越不同应用系统的对象体系、运行平台、开发语言等的界限,并以服务的形式封装,对外、对内发布应用服务接口,供其他的应用程序调用,从而形成一个基于Web的服务共享平台。     

A design of RFTOG model for distributed real-time applications

In this paper, we design the Real-Time Fault-Tolerant Object Group (RFTOG) model that supports the grouping of distributed objects that are required for distributed application. The proposed model basically provides two services. One is the group management service, which supports both consistency maintenance and transparency of the replicated objects with a variety of replication mechanisms. It also provides the load balancing of distributed applications. The other is real-time service in an object group. When the clients request the service to the service object selected through the load balance, this service guarantees the service execution within deadline for the clients’ requests. We develop the Naval Air Defense System (NADS) simulator for verifying the effectiveness of the services proposed by the RFTOG model.     

Introducing QoS awareness in distributed programming: QTcl

A number of distributed applications require communication services with quality of service (QoS) guarantees. Building global‐scale distributed systems with predictable properties is one of the great challenges for computer systems engineering in the new century. Work undertaken within the Internet Engineering Task Force has led to the definition of novel architectural models for the Internet with QoS support. According to these models, the network has to be appropriately configured in order to provide applications with the required performance guarantees. In next‐generation networks, enabling applications to interact with the underlying QoS services is of primary importance. Hence, several special‐purpose application programming interfaces (APIs) have been defined to let applications negotiate QoS parameters across QoS‐capable networks. However, so far, none of these APIs are available in different operating environments. We believe that such features should be embedded in programming environments for distributed applications. In this work we present how we included QoS control features in Tcl, a programming language that has been widely adopted for the development of distributed multimedia applications. Our work has led to the implementation of QTcl, an extended Tcl interpreter that provides programmers with a new set of primitives, in full compliance with the standard SCRAPI programming interface for the RSVP protocol. QTcl in highly portable, in that it enables standard QoS negotiation to be performed in a seamless fashion on the most common operating systems. Copyright © 2003 John Wiley & Sons, Ltd.     

P2P data replication and trustworthiness for a JXTA-Overlay P2P system using fuzzy logic

P2P systems are very important for future distributed systems and applications. In such systems, the computational burden of the system can be distributed to peer nodes of the system. Therefore, in decentralized systems users become themselves actors by sharing, contributing and controlling the resources of the system. This characteristic makes P2P systems very interesting for the development of decentralized applications. Data replication techniques are commonplace in P2P systems. Data replication means storing copies of the same data at multiple peers thus improving availability and scalability. The trustworthiness of peers also is very important for safe communication in P2P system. The trustworthiness of a peer can be evaluated based on the reputation and actual behaviour of peers to provide services to other peers. In this paper, we propose two fuzzy-based systems for data replication and peer trustworthiness for JXTA-Overlay P2P platform. The simulation results have shown that in the first system, replication factor increases proportionally with increase of number of documents per peer, replication percentage and scale of replication per peer parameters and the second system can be used successfully to select the most reliable peer candidate to execute the tasks.     

Fine-grained visualization pipelines and lazy functional languages

The pipeline model in visualization has evolved from a conceptual model of data processing into a widely used architecture for implementing visualization systems. In the process, a number of capabilities have been introduced, including streaming of data in chunks, distributed pipelines, and demand-driven processing. Visualization systems have invariably built on stateful programming technologies, and these capabilities have had to be implemented explicitly within the lower layers of a complex hierarchy of services. The good news for developers is that applications built on top of this hierarchy can access these capabilities without concern for how they are implemented. The bad news is that by freezing capabilities into low-level services expressive power and flexibility is lost. In this paper we express visualization systems in a programming language that more naturally supports this kind of processing model. Lazy functional languages support fine-grained demand-driven processing, a natural form of streaming, and pipeline-like function composition for assembling applications. The technology thus appears well suited to visualization applications. Using surface extraction algorithms as illustrative examples, and the lazy functional language Haskell, we argue the benefits of clear and concise expression combined with fine-grained, demand-driven computation. Just as visualization provides insight into data, functional abstraction provides new insight into visualization.     

Colony: An Artificial Life Model for Active Autonomous Objects

Appropriate aids on top of the primitive object-oriented model will help promote better understanding of the semantics of applications and allow us to focus better on the various aspects of given problems. This study focuses on the exploration of a design model and the corresponding programming framework for the modelling and implementation of applications involving active autonomous objects based on the object technology. The proposed design model is an artificial life model based on the colony phenomenon in nature. This model can naturally be mapped onto an object-oriented implementation. The colony model favours a predicate-based object communication/coordination pattern as opposed to the navigational message-passing paradigm seen in programming languages such as C+ +. The proposed model is particularly appealing to us, for it presents a unifying conceptual design model and programming framework for a wide class of applications including neural networks, genetic algorithms and fuzzy expert systems. The ideas presented are illustrated through a genetic algorithm problem.     

基于Web Service的上海/巴符州科技经济信息通道的设计

作为下一代Web标志性技术的WebService克服了传统构建技术的弊端，提出了，一种新的面向服务的体系结构．它能够跨越应川系统的对象体系、运行环境、开发语言等技术方而的界限，建立高效的电子商务运行环境。该文在对WebService模型深入分析研究的基础上，用WebService的技术对上海／巴符州科技经济信息通道进行设计。     

分布对象平台Java RMI和CORBA的对比研究

文章对开发基于Java的分布式应用程序的两种分布对象技术—————JavaRMI和CORBA的功能和效率进行了对比和分析。CORBA具有良好的语言中立性,定义有功能较强的各种服务,适合于规模较大,需要与其他语言集成的系统,它的缺点是开发过程较为繁琐,Java的一些先进特性无法在远程调用的界面上使用。RMI与Java语言结合得十分紧密,开发方便,支持对象传值,但它不太适合需要异种语言集成的场合。     

Modules,objects and distributed programming: Issues in RPC and remote object invocation

Distributed programming can be greatly simplified by language support for distributed communication, such as that provided by remote procedure call (RPC) or remote object invocation. This paper examines design and implementation issues in these systems, and focuses on the influence of the communication system on a distributed program. To make the discussion concrete, we introduce a single application as implemented in two environments: Modula-2+, an extension of Modula-2 with RPC, and Emerald, an object-based language that supports remote object invocation. We show that small differences in the implementation of the communication system can have a significant impact on how distributed applications are structured.     

An ECA object service to support active distributed objects

Existing Object Management Group (OMG) standards (such as the Common Object Request Broker Architecture specification) provide specific details on how to model distributed objects through the use of an object request broker. However, the specification provided by OMG is not sufficient. For example, it does not specify how active, distributed objects can perform certain functions in response to certain events. It also does not provide any details on how to implement an object service to support active, distributed objects. Such an object service can provide facilities for applications to define events and rules. In view of this, this paper identifies, explores, and provides an approach to model applications as active, distributed objects. The research specifically involves the design, development, and experimental demonstration of an object service based on an active, distributed object model. This object service allows applications to define events and rules. When an event occurs, the object service locates the rule objects and triggers them. It also provides transparency for the objects which generate events. To provide a specific context for the approach, an object service using the specifications provided by the OMG is designed and implemented. The class of application environments for which this approach is suitable and useful includes time-dependent applications and systems that require some form of action such as medical and geographic information systems, distributed work-flow management, distributed expert systems, and computer-integrated manufacturing.     

基于WebService的WebGIS的设计与应用

基于WebGIS目前存在的一些不足,提出构建基于WebService的WebGIS系统,并说明这种系统的优势和特点。通过对正在开发的基于WebService的WebGIS系统的设计和一些已经完成的工作的介绍,来说明系统的可行性和先进性。     

基于CORBA的分布式多媒体服务的QoS模型

对于分布式多媒体来说,必须保证包括端系统、通讯系统以及网络在内的整个系统的服务质量（QoS）。CORBA提供了一个开放式的分布式对象计算环境,它能使许多普通的网络程序设计自动化,并允许应用在异构环境下无缝链接。文章根据分布式多媒体通讯系统中的层次结构模型（QOS－A）,提出了一种基于CORBA的分布式多媒体模型。     

Active Data: A programming model to manage data life cycle across heterogeneous systems and infrastructures

The Big Data challenge consists in managing, storing, analyzing and visualizing these huge and ever growing data sets to extract sense and knowledge. As the volume of data grows exponentially, the management of these data becomes more complex in proportion. A key point is to handle the complexity of the data life cycle, i.e. the various operations performed on data: transfer, archiving, replication, deletion, etc. Indeed, data-intensive applications span over a large variety of devices and e-infrastructures which implies that many systems are involved in data management and processing. We propose Active Data, a programming model to automate and improve the expressiveness of data management applications. We first define the concept of data life cycle and introduce a formal model that allows to expose data life cycle across heterogeneous systems and infrastructures. The Active Data programming model allows code execution at each stage of the data life cycle: routines provided by programmers are executed when a set of events (creation, replication, transfer, deletion) happen to any data. We implement and evaluate the model with four use cases: a storage cache to Amazon-S3, a cooperative sensor network, an incremental implementation of the MapReduce programming model and automated data provenance tracking across heterogeneous systems. Altogether, these scenarios illustrate the adequateness of the model to program applications that manage distributed and dynamic data sets. We also show that applications that do not leverage on data life cycle can still benefit from Active Data to improve their performances.