远程过程调用的实现,应用与问题

分布式软件随着分布式计算的盛行而日益增多与丰富，既有支持分布式计算的系统软件环境，也包括不断涌现的各类应用软件。远程过程与远程过程调用（ＲＰＯ在分布式软件的构成和功能实现上起着关键作用，许多分布式计算软件环境及应用系统大都用ＲＰＣ方式实现。本文介绍ＲＰＣ的产生、实现与各种应用，并讨论ＲＰＣ发展与使用中的几个问题。     

Design and implementation of efficient communication abstractions on the Virtual Interface Architecture: Stream sockets and RPC experience

The emergence and standardization of system area networks (SANs) has provided distributed applications with a medium for high‐bandwidth, low‐latency communication. Standard user‐level networking architecture such as the Virtual Interface (VI) Architecture enables distributed applications to perform low overhead communication over SANs. The VI Architecture significantly reduces system processing overheads and provides each consumer process with a protected, directly accessible interface to the network hardware. Developing distributed applications using low‐level primitives provided by user‐level networking architecture like the VI Architecture is complex and requires significant effort. This paper describes how high‐level communication paradigms like stream sockets and remote procedure call (RPC) can be efficiently built over the VI Architecture. To evaluate performance benefits for standard client–server and multi‐threaded environments, our focus is on off‐the‐shelf sockets and RPC interfaces and commercially available VI Architecture‐based SANs. The key design techniques developed in this paper include credit‐based flow control, decentralized user‐level protocol processing, caching of pinned communication buffers, and deferred processing of completed send operations. In the experimental evaluation, the one‐way bandwidth achieved by stream sockets over VI Architecture was three to four times better than the bandwidth achieved by running legacy protocols over the same interconnect. On the same SAN, high‐performance stream sockets and RPC over VI Architecture achieve significantly better (between 2× and 3× less) latency than conventional stream sockets and RPC over standard networking protocols in a Windows NT? 4.0 environment. Furthermore, our high‐performance RPC transparently improved the network performance of the distributed component object model (DCOM) by a factor of two to three. Copyright © 2001 John Wiley & Sons, Ltd.     

Embedded software debugging using virtual filesystem abstractions

We present a scalable technique to simplify the software debugging process for embedded systems that is based on the use of distributed filesystem abstractions. In this technique, the principal building blocks within embedded systems comprising “system-on-chip” (SoC) devices export debugging interfaces realized with filesystem abstractions. These filesystem interfaces are composed in a manner consistent with the hardware hierarchy and provide a portable interface to concurrently debug software executing in the various processing elements within the embedded system. We illustrate application of the model to support the various software debugging requirements unique to SoCs, many of which traditional methods are ill-equipped to deal with. We also present an architecture that may be used to realize distributed filesystem abstractions within resource constrained embedded architectures.     

A Java-centric Distributed Object-based Paradigm for Surveillance Services and Visual Message Exchange

Building an effective surveillance system on the Internet is an interesting application involving the interoperability of heterogeneous computing environments and the challenge of orchestrating the exchange of different visual message types in a unified manner. In this paper, we propose a distributed object-based paradigm to achieve this by applying the so-called bridging technologies for supporting distributed surveillance services. This paradigm integrates emerging technologies of the next-generation Internet-based applications ranging from wireless transmission at the network infrastructure level, to multi-tier, client/server, and RMI/CORBA at the architecture level, and to Java-centric, delegation-based visual user interfaces, and object web-based user interfaces at the system design level. The experimental results show that objects in the paradigm can efficiently cross the boundaries of different platforms, operating systems, programming languages, and visual message types. The DSS paradigm establishes a firm basis for supporting a variety of potentially cost-effective applications in a plug-and-play manner.     

Model-driven architecture-centric engineering of (embedded) software intensive systems: modeling theories and architectural milestones

Today, in general, embedded software is distributed onto networks and structured into logical components that interact asynchronously by exchanging messages. The software system is connected to sensors, actuators, human machine interfaces and networks. In this paper we study fundamental models of composed embedded software systems and their properties, identify and describe various basic views, and show how they are related. We consider, in particular, models of data, states, interfaces, functionality, hierarchically composed systems, and processes. We study relationships by abstraction and refinement as well as forms of composition and modularity. In particular, we introduce a comprehensive mathematical model and a corresponding mathematical theory for composed systems, its essential views and their relationships. We introduce two methodologically essential, complementary and orthogonal concepts for the structured modeling of multifunctional embedded systems in software and systems engineering and their scientific foundation. One approach addresses mainly tasks in requirements engineering and the specification of the comprehensive user functionality of multifunctional systems in terms of their functions, features and services. The other approach essentially addresses the design phase with its task to develop logical architectures formed by networks of interactive components that are specified by their interface behavior.     

Infrastructure for Design, Deployment and Experimentation of Distributed Agent-based Systems: The Requirements, The Technologies, and An Example

This paper discusses infrastructure for design, development, and experimentation of multi-agent systems. Multi-agent system design requires determining (1) how domain requirements drive the use of agents and AI techniques, (2) what competencies agents need in a MAS, and (3) which techniques implement those competencies. Deployment requirements include code reuse, parallel development through formal standardized object specifications, multi-language and multi-platform support, simulation and experimentation facilities, and user interfaces to view internal module, agent, and system operations. We discuss how standard infrastructure technologies such as OMG IDL, OMG CORBA, Java, and VRML support these services. Empirical evaluation of complex software systems requires iteration through combinations of experimental parameters and recording desired data. Infrastructure software can ease the setup, running, and analysis of large-scale computational experiments. The development of the Sensible Agent Testbed and architecture over the past six years provides a concrete example. The design rationale for the Sensible Agent architecture emphasizes domain-independent requirements and rapid deployment to new application domains. The Sensible Agent Testbed is a suite of tools providing or assisting in setting up, running, visually monitoring, and chronicling empirical testing and operation of complex, distributed multi-agent systems. A thorough look at the various Sensible Agents infrastructure pieces illustrates the engineering principles essential for multi-agent infrastructure, while documenting the software for users.     

A Knowledge-Based Software Life-Cycle Framework for the Incorporation of Multicriteria Analysis in Intelligent User Interfaces

Decision-making theories aiming at solving decision problems that involve multiple criteria have often been incorporated in knowledge-based systems for the improvement of these systems' reasoning process. However, multicriteria analysis has not been used adequately in intelligent user interfaces, even though user-computer interaction is, by nature, multicriteria-based. The actual process of incorporating multicriteria analysis into an intelligent user interface is neither clearly defined nor adequately described in the literature. It involves many experimental studies throughout the software life-cycle. Moreover, each multicriteria decision-making theory requires different kinds of experiments for the criteria to be determined and then for the proper respective weight of each criterion to be specified. In our research, we address the complex issue of developing intelligent user interfaces that are based on multicriteria decision-making theories. In particular, we present and discuss a software life-cycle framework that is appropriate for the development of such user interfaces. The life-cycle framework is called MBIUI. Given the fact, that very little has been reported in the literature about the required experimental studies, their participants and the appropriate life-cycle phase during which the experimental studies should take place, MBIUI provides useful insight for future developments of intelligent user interfaces that incorporate multicriteria theories. One significant advantage of MBIUI is that it provides a unifying life-cycle framework that may be used for the application of many different multicriteria decision-making theories. In the paper, we discuss the incorporation features of four distinct multicriteria theories: TOPSIS, SAW, MAUT, and DEA. Furthermore, we give detailed specifications of the experiments that should take place and reveal their similarities and differences with respect to the theories.     

Integrating Computing Resources on Multiple Grid-Enabled Job Scheduling Systems Through a Grid RPC System

We present a framework for a parallel programming model by remote procedure calls, which bridge large-scale computing resource pools managed by multiple Grid-enabled job scheduling systems. With this system, the user can exploit not only remote servers and clusters, but also the computing resources provided by Grid-enabled job scheduling systems located on different sites. This framework requires a Grid remote procedure call (RPC) system to decouple the computation in a remote node from the Grid RPC mechanism and uses document-based communication rather than connection-based communication. We implemented the proposed framework as an extension of the OmniRPC system, which is a Grid RPC system for parallel programming. We designed a general interface to easily adapt the OmniRPC system to various Grid-enabled job scheduling systems, including XtremWeb, CyberGRIP, Condor and Grid Engine. We show the preliminary performance of these implementations using a phylogenetic application. We found that the proposed system can achieve approximately the same performance as OmniRPC and can handle interruptions in worker programs on remote nodes. Yoshihiro Nakajima is a Research Fellow of the Japan Society for the Promotion of Science     

The performance of the Amoeba distributed operating system

Amoeba is a capability-based distributed operating system designed for high-performance interactions between clients and servers using the well-known RPC model. The paper starts out by describing the architecture of the Amoeba system, which is typified by specialized components such as workstations, several services, a processor pool, and gateways that connect other Amoeba systems transparently over wide-area networks. Next the RPC interface is described. The paper presents performance measurements of the Amoeba RPC on unloaded and loaded systems. The time to perform the simplest RPC between two user processes has been measured to be 1-4 ms. Compared to SUN 3/50's RPC, Amoeba has one ninth of the delay, and over three times the throughput. Finally we describe the Amoeba file server. The Amoeba file server is so fast that it is limited by the communication bandwidth. To the best of our knowledge this is the fastest file server yet reported in the literature for this class of hardware.     

From user interface design to the support of intelligent and adaptive interfaces: an overhaul of user interface software infrastracture

Research on adaptive interfaces in the past has lacked support from user interface tools which allow interfaces to be easily created and modified. Also, current user interface tools provide no support for user models which can collect task-oriented information about users. Developing an adaptive interface requires a user model and an adaptation strategy. It also, however, requires a user interface which can be adapted. The latter task is often time-consuming, especially in relation to more sophisticated user interfaces.

The paper presents a user interface design environment, UIDE, which has a different software infrastracture. Designers use high-level specifications to create a model of an application and links from the application to various interface components. The model is the heart of all the design and run-time support in UIDE, including automatic dialog sequencing and help generation. UIDE provides automatic support for collecting task-oriented information about users, by the use of its high-level specifications in its application model as a basic construct for a user model. Some examples of adaptive interfaces and adaptive help are presented that use the information that is collectable in UIDE.     

Contributions of Dichotomic View of plasticity to seamlessly embed accessibility and adaptivity support in user interfaces

Recent legal changes have increased the need for developing accessible user interfaces in computer-based systems. In this sense, previously existing user interfaces are intended to be modified and new user interfaces are intended to be designed taking accessibility guidelines into account. Typically, model-based approaches have been used when developing accessible user interfaces or redefining existing ones. But the use of static models leads to the development of not dynamically adaptable user interfaces. Dynamic adaptation in accessible user interfaces is important due to the fact that interaction difficulties on people with disabilities may change through use. In this paper, we present some contributions that can be obtained from the application of the Dichotomic View of plasticity in the personalization of user interfaces. With the double perspective defined in this approach, it is intended to go further from a mere adaptation to certain user stereotypes, offering also a dynamic support to real limitations or difficulties users can encounter during the use of the UI. This goal is achieved analyzing user logs by an inference engine that dynamically infers modifications in the user interface to adjust it to varying user needs. A case study is presented in order to show how the guidelines and software support defined in the Dichotomic View of plasticity can be applied to develop a component for a particular system aimed at performing dynamic user interface adaptations with accessibility purposes. This approach includes some innovations that make it different from conventional adaptable mechanisms applied to accessibility in some important aspects.     

A coordination framework and architecture for internet groupware

We discuss a group coordination architecture to support Internet-wide distributed collaboration, in particular for WWW-based distance education. With the current surge in e-commerce and Web-centric information exchange among users, the need for systems offering better telepresence and interaction capabilities becomes tangible. Group coordination in distributed systems and networked multimedia systems has many faces manifested in a variety of user interfaces and network protocols. However, to date no general methodology exists for engineering group coordination protocols to streamline the deployment of remote learning and collaboration environments. The objective of this article is to identify the key elements of a general group coordination framework, complementing existing group membership and multicast dissemination models, and to set the cornerstones for a coordination architecture which may be used to leverage the rapid development of group-oriented distributed collaborative applications in the Internet, for example for distance education, distributed scientific simulation and visualization, or similar applications.     

The user modeling shell system BGP-MS

BGP-MS is a user modeling shell system that can assist interactive software systems in adapting to their current users by taking the users' presumed knowledge, beliefs, and goals into account. It offers applications several methods for communicating observations concerning the user to BGP-MS, and for obtaining information on currently held assumptions about the user from BGP-MS. It provides a choice of two integrated formalisms for representing beliefs and goals, and includes several types of inferences for drawing additional assumptions based on an initial interview, observed user actions, and stereotypical knowledge about pre-defined user subgroups. BGP-MS is a customizable software system that is independent from applications, operates concurrently with them, and interacts with them through inter-process communication. For tailoring BGP-MS to a specific application domain, the developer must select those components of BGP-MS that are needed in this domain and fill them with relevant domain-dependent user modeling knowledge. This paper first summarizes the user modeling services that BGP-MS provides to application programs at runtime. It discusses the representational and inferential foundations that determine the scope and the limits of these services, and also gives a detailed example illustrating the interaction between the various system components. It describes interfaces that are available to application developers for tailoring BGP-MS to the specific user modeling needs of their application domains. Finally, it compares the system with all other major user modeling shell systems, and describes a first application that employs BGP-MS for adapting hypertext to users' terminological knowledge.The managing UMUAI editor for this paper was Sandra Carberry, University of Delaware.     

An analysis of the use of natural language processing systems in business

. The results of a survey conducted amongst managers, users and application developers of Natural Language interrogation systems are presented and analysed. Those that were able to develop successful and effective applications using natural language paid careful attention to the certain stages. It is proposed that these stages are: 1. Systematic analysis of the company's requirements. 2. Effective integration of the natural language technology with the target database ensuring current applications are not adversely affected. 3. Introduction to new users of the system. This resulted in realistic user expectations and enabled effective use of the natural language software. The advantages and disadvantages of natural language interfaces from an application developer, manager and user perspective are also discussed and recommendations made.     

Designing an agent synthesis system for cross-RPC communication

Remote procedure call (RPC) is the most popular paradigm used today to build distributed systems and applications. As a consequence, the term “RPC” has grown to include a range of vastly different protocols above the transport layer. A resulting problem is that programs often use different RPC protocols, cannot be interconnected directly, and building a solution for each case in a large heterogeneous environment is prohibitively expensive. We describe the design of a system that can synthesize programs (RPC agents) to accommodate RPC heterogeneities. Because of its synthesis capability, the system also facilitates the design and implementation of new RPC protocols through rapid prototyping. We have built a prototype system to validate the design and to estimate the agent development costs and cross-RPC performance. The evaluation shows that the synthesis approach provides a more general solution than existing approaches do, and with lower software development and maintenance costs, while maintaining reasonable cross-RPC performance     

Adaptive,intelligent presentation of information for the museum visitor in PEACH

The study of intelligent user interfaces and user modeling and adaptation is well suited for augmenting educational visits to museums. We have defined a novel integrated framework for museum visits and claim that such a framework is essential in such a vast domain that inherently implies complex interactivity. We found that it requires a significant investment in software and hardware infrastructure, design and implementation of intelligent interfaces, and a systematic and iterative evaluation of the design and functionality of user interfaces, involving actual visitors at every stage. We defined and built a suite of interactive and user-adaptive technologies for museum visitors, which was then evaluated at the Buonconsiglio Castle in Trento, Italy: (1) animated agents that help motivate visitors and focus their attention when necessary, (2) automatically generated, adaptive video documentaries on mobile devices, and (3) automatically generated post-visit summaries that reflect the individual interests of visitors as determined by their behavior and choices during their visit. These components are supported by underlying user modeling and inference mechanisms that allow for adaptivity and personalization. Novel software infrastructure allows for agent connectivity and fusion of multiple positioning data streams in the museum space. We conducted several experiments, focusing on various aspects of PEACH. In one, conducted with 110 visitors, we found evidence that even older users are comfortable interacting with a major component of the system.     

A Java/CORBA virtual machine architecture for remote execution of optimization solvers in heterogeneous networks

Virtual machines for remote execution are a useful tool for utilizing light user interfaces and intensive application cores in different physical machines connected through the Internet. In a virtual machine, application cores are distributed in a network. Specific locations, operating systems and hardware characteristics are hidden by virtual machines. They make it possible to use a PC to execute user interfaces and (a few) high‐performance computers for application cores. We present a Java/CORBA‐based brokerage platform that allows remote execution of optimization solvers from a client running on any platform. The system offers a dynamic library of available problem solvers, and a graphic interface to browse several defined properties and metadata on available solvers. In addition, an embedded file compression module to reduce data transfer time is included as a plug‐in feature of the proposed virtual machine. Analogous systems could be constructed for applications in which interaction traffic time is much lower than execution time. Copyright © 2001 John Wiley & Sons, Ltd.     

A formal model for plastic human computer interfaces

The considerable and significant progress achieved in the design and development of new interaction devices between man and machine has enabled the emergence of various powerful and efficient input and/or output devices. Each of these new devices brings specific interaction modes.With the emergence of these devices, new interaction techniques and modes arise and new interaction capabilities are offered. New user interfaces need to be designed or former ones need to evolve. The design of so called plastic user interfaces contributes to handling such evolutions. The key requirement for the design of such a user interface is that the new obtained user interface shall be adapted to the application and have, at least, the same behavior as the previous (adapted) one. This paper proposes to address the problem of user interface evolution due to the introduction of new interaction devices and/or new interaction modes. More, precisely, we are interested by the study of the design process of a user interface resulting from the evolution of a former user interface due to the introduction of new devices and/or new interaction capabilities. We consider that interface behaviors are described by labelled transition systems and comparison between user interfaces is handled by an extended definition of the bi-simulation relationship to compare user interface behaviors when interaction modes are replaced by new ones.     

Software environment architectures and user interface facilities

The authors discuss the demands and constraints on a user interface management system for a software environment, and the relation between the architecture of the environment and the user interface management system. A model for designing user interface management systems for large extensible environments is presented. This model synthesizes several recent advances in user interfaces and specializes them to the domain of software environments. The model can be applied to a wide variety of environment contexts. A prototype implementation is described