Distributed Computing Environment Research Articles

Vers un modèle générique d’assistance aux acteurs du téléapprentissage

A generic model of assistance for telelearning actors is presented. The help system described by this model can be linked to any distributed or local computer environment, regardless type of knowledge domain and type of online users (learner, designer, tutor, teacher, etc.) using the help system. The help system guides these users by offering advice or by adapting the interface according to their preferences or those of a work team, to their task progress, to their interaction and/ or to their history of utilized help functions in the help system. The generic model identifies the various components of such a system and proposes several typologies (help access types, object types, type of goals and themes, types of help conditions and actions, etc.). An applied example of this generic model is presented in order to specify a help system designed for telelearning designers.

Migration of DCE applications into CORBA and SOAP environments

AbstractLegacy applications based on the Distributed Computing Environment (DCE) are subject to several significant limitations. As the development and support of DCE wanes, object‐oriented development becomes more desirable, and transmission over HTTP is established as the preferred protocol over the Internet, DCE application managers and developers are pressed to find extensions and alternatives to DCE. This paper briefly discusses several alternative targets for migration of DCE systems, then proceeds to detail, compare, and contrast two preferred candidates: CORBA and SOAP. Although we have found that developing a general migration solution for legacy DCE applications to CORBA or SOAP to be a non‐trivial, long‐term project, developing specific solutions that are based on a general architecture is feasible. Given a short list of reasonable premises, many DCE applications may be ported to technologies such as CORBA and SOAP. Copyright © 2002 John Wiley & Sons, Ltd.

Agent cooperation based control integration by activity-sharing and joint intention

In this paper, a control integration method based on agent cooperation, called ASOJI, is proposed, which designs the architecture of integrated application systems in distributed computation environments as an agent community composed of nested agent federations in three aspects: architecture style, agent cooperation, and composition semantics. Through defining activity-sharing-oriented joint intention in the way of stepwise refinement, ASOJI can not only support the transparent specification of the architecture for software composition, but also eliminate the gap between agent theory and the engineering realization of control integration.

An Analytic Model of Web Servers in Distributed Computing Environments

Web technologies are currently being employed to provide end-user interfaces in diverse computing environments. The core element of these Web solutions is a Web server based on the HyperText Transfer Protocol (HTTP) running over TCP/IP. Web servers are required to perform millions of transaction requests per day at an acceptable Quality of Service (QoS) level in terms of client response time and server throughput. Consequently, a thorough understanding of the performance capabilities and limitations of Web servers is critical. In many applications, the Web server performs significant dynamic server-side processing in distributed computing environments. In these applications, a Web server retrieves a file, parses the file for scripting language content, interprets the scripting statements, and executes embedded code, possibly requiring a TCP connection to a remote application for data processing and transfer. Web server performance in a distributed environment is a complex interplay between a variety of factors. Although testing is essential for assessing performance, there are inherent limitations to a testing approach for validating Web server performance. Consequently, modeling is critical to further understand the performance capabilities and limitations of Web servers that participate in distributed computing. In this paper, we illustrate a model-based approach to Web server performance evaluation, and present an analytic queueing model of Web servers in distributed environments. Performance predictions from the analytic model match well with the performance observed from simulation. The model forms an excellent basis for a decision support tool to allow system architects to predict the behavior of new systems prior to deployment, or existing systems under new workload scenarios.

A field-based collaboration strategy in MADCE

In this paper, we propose a field-based collaboration algorithm that can be applied to searching the local-best co-agent within field. The dynamic "field" structure of the collaborating objects limits the range of information communicating and sharing, and adjusts the load of Agents dynamically. An efficient method for Agent's collaboration in MADCE is presented, which can balance the system load, reduce the executive cost, and broaden the ability of Distributed Computing Environment.

Auditing Causal Relationships of Group Multicast Communications in Group-Oriented Distributed Systems

Auditability is a crucial aspect of distributed computing security. In a distributed computation environment, we may therefore want to prevent corrupt processes from denying or forging causal relat...

An integrated knowledge representation scheme and query processing mechanism for fault diagnosis in heterogeneous manufacturing environments

An integrated fault diagnosis system was developed for manufacturing complex products, e.g., automobile, that undergo a variety of production processes. The proposed global knowledge representation scheme is designed to consistently express such heterogeneous diagnostic knowledge in terms of the causal relations among relevant attributes across different processes. This scheme is unifying in that it reflects the fact that an effect for one causal relation may in turn be a cause for another along a chain of subsequent processes. In order to unify independent pieces of causal relation, specific attributes of machine-processed products in addition to the usual diagnostic signals such as noise and voltage of the machines. The accompanying probabilistic diagnosis mechanism can then produce an enhanced diagnostic accuracy over other existing schemes as it can simultaneously consider multiple causes of a fault along with their interdependency. The proposed diagnosis mechanism was implemented in a distributed computer environment to identify the functions and procedures required for its actual application.

FADI: A fault tolerant environment for open distributed computing

FADI (FAult tolerant DIstributed environment) is a complete programming environment for the reliable execution of distributed application programs. FADI encompasses all aspects of modern fault-tolerant distributed computing. The built-in user-transparent error detection mechanism covers processor node crashes and hardware transient failures. The mechanism also integrates user-assisted error checks into the system failure model. The nucleus non-blocking checkpointing mechanism combined with a novel selective message logging technique delivers an efficient, low-overhead backup and recovery mechanism for distributed processes. FADI also provides a means of remote automatic process allocation on distributed system nodes.

Distributed Object Environment: Using International Standards for Data Exchange in the Construction Industry

As a contribution to the international efforts toward the development of an integrated technology (IT) for managing project information, a major research project has been undertaken at the University of Salford. Based on advances in international standards in data models, i.e., the Industry Foundation Classes (IFCs), and communication protocols, i.e., the Common Object Request Broker Architecture (CORBA), this project has successfully developed and implemented a three‐tier computer architecture environment to integrated design and construction applications. The IFC data model has been implemented as the single project database in an open and distributed computer environment whereby the World Wide Web has been used as the delivery medium. This article explains the background of this project, outlines other international efforts in this field, introduces the concept of the three‐tier computer architecture, and discusses the proposed structure for the integrated environment along with its implementation issues.

Computer Simulation of a Novel Photocatalytic Reactor Using Distributive Computing Environment

In this paper, the numerical simulation for the in situ degradation of toxic water pollutants in the presence of semiconductor catalyst particles is considered. The computer simulation is in search of an efficient photocatalytic reactor design to achieve better fluid-catalyst contacting to minimize mass transfer limitation. In addition, in the present work, a state-of-the-art efficient computational technique, namely, distributed computing, has been employed to expedite the speed of calculation and overcome the memory bottleneck present in a single workstation. A comparative study has also been made of the computational effort required for a serial, parallel and distributed computing environment. The results show that the distributed computing technique is an economical and efficient method for overcoming difficulties, such as the memory bottleneck present in single workstations and the long computation time, associated with computer simulations of reacting flows.

Scalable networked information processing environment (SNIPE)

Scalable Networked Information Processing Environment (SNIPE) is a metacomputing system that aims to provide a reliable, secure, fault-tolerant environment for long-term distributed computing applications and data stores across the global Internet. This system combines global naming and replication of both processing and data to support large-scale information processing applications leading to better availability and reliability than currently available with typical cluster computing and/or distributed computer environments. To facilitate this the system supports: distributed data collection, distributed computation, distributed control and resource management, distributed output and process migration. The underlying system supports multiple communication paths, media and routing methods to aid performance and robustness across both local and global networks. This paper details the goals, design and an initial implementation of SNIPE, and then demonstrates its usefulness in supporting a middleware project. Initial communications performance is also presented.

A Distributed Computing Environment for Dynamic Traffic Operations

This study explores distributed computing techniques in the context of dynamic network algorithms for intelligent transportation systems (ITS) applications. ITS technologies such as Advanced Traveler Information Systems (ATIS) and Advanced Traffic Management Systems (ATMS) provide traffic-related information on-line for a new generation of models and methodologies that aim at the real-time enhancement of network performance and efficiency. To address the problem of the severe computational burden of processing network-wide time-dependent traffic-related data (such as volume, speed, occupancy, and classification), the authors investigate two remote procedure call (RPC) - based distributed computing techniques on a network of workstations. Computational results indicate that the distributed implementation performs better than sequential computation, although tradeoffs between communications overheads and computational savings become critical with the number of processors.

Editorial: Applications of Distributed Computing Environments

Editorial: Applications of Distributed Computing Environments

Editorial: Applications of Distributed Computing Environments

Editorial: Applications of Distributed Computing Environments

Decentralized Work ow Management: Architecture and Components

This contribution describes the need for decentralized and autonomous Work ow Management Systems (WfMS) and current technologies for their realization. An own, DCE (Distributed Computing Environment) based approach is presented and crucial architectu

A Parallel Recursive Shortest Spanning Tree Algorithm for Image Segmentation in Distributed Computing Environment

The recursive shortest spanning tree (RSST) algorithm has been used for various image and video coding systems. The speed is very demanding for such applications. However, the RSST algorithm is too complex to perform in a reasonable time. This motivates the present work. A distributed algorithm that constructs a recursive shortest spanning tree for image segmentation with a fixed number of processors is presented in this paper. Using a tailored data partition strategy to assign jobs to processors in our proposed parallel recursive shortest spanning tree (PRSST) algorithm, we derive a new lower bound ofO(n) for one processor with ann-pixel image. The complexity of the proposed algorithm is cost-optimal and the total number of messages required isO(c) for images of any size, wherecis a small constant. The objective quality of segmented images produced by our PRSST has maximum 1.5 dB difference from those generated by Morris's RSST algorithm for images of the size of 128 by 128 and 150 by 150 pixels.

Tools for remote collaboration on the DIII-D National Fusion Facility

The DIII-D National Fusion Facility, a tokamak experiment funded by the US Department of Energy and operated by General Atomics (GA), is an international resource for plasma physics and fusion energy science research. This facility has a long history of collaborations with scientists from a wide variety of laboratories and universities from around the world. That collaboration has mostly been conducted by travel to and participation at the DIII-D site. Many new developments in the computing and technology fields are now facilitating collaboration from remote sites, thus reducing some of the needs to travel to the experiment. Some of these developments include higher speed wide area networks, powerful workstations connected within a distributed computing environment, network based audio/video capabilities, and the use of the world wide web. As the number of collaborators increases, the need for remote tools become important options to efficiently utilize the DIII-D facility. In the last two years a joint study by GA, Princeton Plasma Physics Laboratory (PPPL), Lawrence Livermore National Laboratory (LLNL), and Oak Ridge National Laboratory (ORNL) has introduced remote collaboration tools into the DIII-D environment and studied their effectiveness. These tools have included the use of audio/video for communication from the DIII-D control room, the broadcast of meetings, use of inter-process communication software to post events to the network during a tokamak shot, the creation of a DCE (distributed computing environment) cell for creating a common collaboratory environment, distributed use of computer cycles, remote data access, and remote display of results. This study also included sociological studies of how scientists in this environment work together as well as apart. As a result of these studies, there is now in place an automated distributed processing environment connected to the real-time experimental operations which can be joined by users at remote locations. This environment will allow further exploration of the technology and sociology of remote participation in the DIII-D program. Having the tools in place has already permitted remote participation in DIII-D experiments that would not have occurred otherwise, and thus the introduction of these tools has shown the initial feasibility of increasing and improving remote collaboration.

Managing complexity: middleware explained

Traditionally, most definitions seeking to characterize middleware suggest that it is the software that facilitates remote database access and systems transactions. More recently, the term has come to be associated-somewhat limitingly-with distributed platforms such as the Open Software Foundation's Distributed Computing Environment (DCE) and the Object Management Group's Common Object Request Broker Architecture (CORBA). And some have loosely applied it to systems as diverse as workflow support environments and even to the Web itself. We believe the essential role of middleware is to manage the complexity and heterogeneity of distributed infrastructures and thereby provide a simpler programming environment for distributed-application developers. It is therefore most useful to define middleware as any software layer that is placed above the distributed system's infrastructure-the network OS and APIs-and below the application layer.

A framework for analysing decisions under risk

The main objective is to present a framework for analysing decisions under risk. The nature of much information available to decision makers is vague and imprecise, be it information for human managers in organisations or for process agents in a distributed computer environment. Some approaches address the problem of uncertainty, but many of them concentrate more on representation and less on evaluation. The emphasis in this paper is on evaluation and even though the representation used is that of probability theory, other well-established formalisms can be used. The approach allows the decision maker to be as deliberately imprecise as he feels is natural and provides him with the means for expressing varying degrees of imprecision in the input sentences. The framework we present is intended to be tolerant and to provide means for evaluating decision situations using several decision rules beside the conventional maximisation of the expected utility.

Security in Distributed Computing

Glen Bruce and Rob Dempsey Prentice Hall PTR, Upper Saddle River, NJ, 1997, 456 pp. ISBN 0-13-182908-4, $56.00 This book is well written and organized to cover all aspects of computer security, especially in distributed computing environments. The overall computer security problems in computer systems, computer networks and database systems are explained throughout the book. Furthermore, the computer security problems are covered in balance based on the views and approaches of the business and technology sides. The book is organized with four parts. The introductory part 1 begins with a good overview of the security problems in distributed computing environments. In part 2, the foundations of computer security are discussed. Chapter 3 covers computing security basics by using the trust model which consists of identification, authentication, authorization, confidentiality, integrity, nonrepudiation, and so on. Chapter 4 explains the security architecture model which is based on foundation control and trust models. The following chapter 5 illustrates the foundation model that is based on security policy, security principles, security criteria and standards, and education. Chapter 6 discusses security policies based on corporate principles and business code of conduct. In part 3, all aspects of computer security technologies are covered. Chapter 7 begins with the illustration of what is a trusted network, which is followed by the discussions of System Network Architecture (SNA) and Transmission Control Protocol and Internet Protocol (TCP/IP). Chapter 8 explains network operating systems mostly based on Novell’s NetWare as well as other networking operating systems. Chapter 9 illustrates client/server system and Common Object Request Broker Architecture (CORBA) briefly. The security problems and possible corresponding solutions are explained well in chapters 10 through 12, which are followed by chapter 13 specifying Windows NT security. Chapter 14 explains the security problems and requirements connecting the network to the Internet by using a firewall machine as an example. Chapter 15 illustrates Data Encryption Standard (DES) private key encryption, and RSA public key encryption which are very well to understand. Chapter 16 covers the Distributed Computing Environment (DCE) from the Open Software Foundation (OSF) which provides the fundamental middleware services that allow clients and servers to work in a secure way. The following chapter 17 enhances the discussion of the fundamental aspects of DCE of chapter 16. Chapter 18 extends to the illustration of the security features in distributed database systems. The last chapter in part 2 explains the On-Line Transaction Processing (OLTP) by using available commercial products. In part 4, chapter 20 begins with how to design client-server applications satisfying security issues discussed in the previous chapters. Chapter 21 shows the examples of applying computer security in electronic mail and groupware. The following chapters 22 and 23 discuss how to manage security in the distributed system environments and how to develop a suitable security strategy for organizations. Chapter 24 explains well about all aspects related to auditing in computer systems. The final chapter of this book concludes with describing the security issues in the future. This book is an important reference book for anyone interested in computer security in distributed computing and especially for those beginners in the computer security field. The book is one of the better computer security books that is easy to follow. Haklin Kimm, University of Tennessee