Showing papers in "Advances in Computers in 1999"

A Survey of Current Paradigms in Machine Translation

Abstract: This paper is a survey of the current machine translation research in the US, Europe and Japan. A short history of machine translation is presented first, followed by an overview of the current research work. Representative examples of a wide range of different approaches adopted by machine translation researchers are presented. These are described in detail along with a discussion of the practicalities of scaling up these approaches for operational environments. In support of this discussion, issues in, and techniques for, evaluating machine translation systems are addressed.

Architectures and Patterns for Developing High-performance, Real-time ORB Endsystems

Abstract: Many types of applications can benefit from flexible and open middleware. CORBA is an emerging middleware standard for Object Request Brokers (ORBs) that simplifies the development of distributed applications and services. Experience with CORBA demonstrates that it is suitable for traditional RPC-style applications. However, the lack of performance optimizations and quality of service (QoS) features in conventional CORBA implementations make them unsuited for high-performance and real-time applications. This paper makes four contributions to the design of CORBA ORBs for applications with high-performance and real-time requirements. First, it describes the design of TAO, which is our high-performance, real-time CORBA-compliant ORB. Second, it presents TAO’s real-time scheduling service, which provides QoS guarantees for deterministic real-time CORBA applications. Third, it empirically evaluates the effects of priority inversion and non-determinism in conventional ORBs and shows how these hazards are avoided in TAO. Fourth, it presents a case study of key patterns used to develop TAO and quantifies the impact of applying patterns to reduce the complexity of common ORB tasks.

3–D Visualization of Software Structure

Abstract: A common and frustrating problem in software engineering is the introduction of new faults as a side-effect of software maintenance. An understanding of all of the relationships that exist between modified software and the rest of a system can limit the introduction of new faults. For large systems, these relationships can be numerous and subtle. The relationships can be especially complex in object-oriented systems that include inheritance and dynamic binding. Software visualization can potentially ease both impact analysis and general program understanding. Software visualization can facilitate program understanding by graphically displaying important software features. However, despite recent success in developing useful and intuitive graphical representations for certain aspects of software, current software visualization systems are limited by their lack of scalability—the ability to visualize both small- and large-scale software entities. This paper demonstrates that three-dimensional (3–D) graphics and a hierarchy of overlapping views can increase the scalability of software visualization. The hierarchy provides detailed information without sacrificing the “big picture.” Overlapping is used to provide context between high- and low-level views. A prototype system, Change Impact Viewer (CIV), tests these visualization mechanisms. CIV highlights areas of a system that can potentially be affected by a change to a selected function. The mechanisms, as implemented in CIV, show improvements in scalability over those provided by other systems, without decreasing usefulness or intuitiveness.

A Taxonomy of Distributed Real-time Control Systems

Abstract: The demands placed on industrial automation systems have grown in many dimensions over the last two decades. Examples of such demands are increased size, functionality, speed, flexibility, simpler programming, quality, and decreased installation and commissioning costs. An emerging approach to meeting such demands is the use of Distributed Real-time Control System (DRCS) architectures and technologies. This chapter discusses key issues that are driving this trend in modern industrial automation systems and provides a framework for discussion and technological research.

Digital Libraries: Social Issues and Technological Advances

Abstract: The location and provision of information services has dramatically changed over the last ten years There is no need to leave the home or office to locate and access information now readily available on-line via digital gateways furnished by a wide variety of information providers, (eg libraries, electronic publishers, businesses, organizations, individuals) Information access is no longer restricted to what is physically available in the nearest library It is electronically accessible from a wide variety of globally distributed information repositories—“digital libraries” In this chapter we will focus on digital libraries, starting with a discussion of the historical visionaries, definitions, driving forces and enabling technologies and some key research issues We will discuss some of the US and international digital library projects and research initiatives We will then describe some of the emerging techniques for building large-scale digital libraries, including a discussion of semantic interoperability, the “Grand Challenge” of digital library research Finally, we offer our conclusions and a discussion of some future directions for digital libraries

Heterogeneous Data Access in a Mobile Environment – Issues and Solutions

Abstract: A mobile computing environment involves accessing information through a wireless network connection. The mobile unit may be stationary, in motion, and/or intermittently connected to a fixed (wired) network. As technology advances are made in software and hardware, the feasibility of accessing information “anytime, anywhere” is becoming a reality. Furthermore, the diversity and amount of information available to a given user is increasing at a rapid rate. Current distributed and multidatabase systems are designed to allow timely and reliable access to large amounts of data from different data sources. Issues such as autonomy, heterogeneity, transaction management, concurrency control, transparency, and query resolution have been addressed by researchers for multidatabase systems. These issues are similar to many of the issues involved in accessing information in a mobile environment. However, in a mobile environment, additional complexities are introduced due to network bandwidth, processing power, energy, and display restrictions inherent in mobile devices. This chapter discusses the fundamental issues involved with mobile data access, the physical environment of mobile systems, and currently implemented mobile solutions. Furthermore, the issues involved in accessing information in a multidatabase environment and mobile computing environment share similarities. Therefore, we propose to superimpose a wireless-mobile computing environment on a multidatabase system in order to realize a system capable of effectively accessing a large amount of data over a wireless medium. We show how one can easily map solutions from one environment to another. This new system is called a mobile data access system (MDAS), which is capable of accessing heterogeneous data sources through both fixed and wireless connections. We will show the feasibility of mapping solutions from one environment to another. Within the scope of this new environment, a new hierarchical concurrency control algorithm is introduced that allows a potentially large number of users to simultaneously access the available data. Current multidatabase concurrency control schemes do not efficiently manage these accesses because they do not address the limited bandwidth and frequent disconnection associated with wireless networks. The proposed concurrency control algorithm—v-lock—uses global locking tables created with semantic information contained within the hierarchy. The locking tables are subsequently used to serialize global transactions, and detect and remove global deadlocks. The performance of the new algorithm is simulated and the results are presented.

Architectures for Mobile Robot Control

Abstract: Effective control of mobile robots and their associated sensors demands the synthesis and satisfaction of several complex constraints and objectives in real-time, particularly in unstructured, unknown, or dynamic environments such as those typically encountered by outdoor mobile robots. For example, an autonomous vehicle may be required to follow roads, drive off-road, follow designated paths, avoid obstacles, and reach goal destinations. To function effectively, an architectural framework for these sensing and reasoning processes must be imposed to provide a structure for combining information from several different sources. Some key issues considered in planning and control architectures are whether they should be centralized or distributed, whether the reasoning should be reactive or deliberative, and whether control should be top-down or bottom-up. In addition, there is a fundamental choice to be made in the method by which information from multiple sources is combined, via sensor fusion or command arbitration. We explore the inherent problems of the mobile robot domain, the nature of the trade-offs that must be considered, consider various types of action selection, and describe some of the solutions that have been proposed and implemented in existing architectures.

Exception-handling Design Patterns

Abstract: Achieving dependable behavior from complex software systems requires that the software logic be able to recover from anomalous conditions or exceptional states. Such conditions and states may arise from embedded defects in the code or from erroneous data provided to the software for processing. One technique for enhancing the ability of software to perform such recovery is the insertion of exception detection and handling features into the logic. Such features may depend on specific exception-handling language facilities or on general-purpose language constructs. This chapter provides an overview of design considerations necessary to implement such recovery, and presents a series of commonly used design patterns that have proved to be successful in enhancing dependable behavior.

Using Domain Models for System Testing

Abstract: Domain models [8, 9, 25] have long been used as a basis for software development and reuse. We present a specialized, simplified domain model that has been used for system testing in industry as the framework for a system testing approach we call application domain-based testing. Sleuth , a test-suite generation tool, is based on this concept. We report on the domain analysis, the domain model components, and industrial experience of reusing domain models and tests generated with Sleuth

The World Wide Web

Abstract: This article provides a high-level overview of the World Wide Web in the context of a wide range of other Internet information access and delivery services. This overview will include client-side, server-side and “user-side” perspectives. Underlying Web technologies as well as current technology extensions to the Web will also be covered. Social implications of Web technology will also be addressed.

Managing Control Asynchrony on SIMD Machines—a Survey

Abstract: The Single Instruction Multiple Data (SIMD) paradigm has several desirable characteristics from the perspective of massively-parallel algorithms. However, its restricted control organization makes it only useful for a small set of applications that fit this restricted model. The alternative for other applications has been to use Multiple Instruction Multiple Data (MIMD) organizations, which are much more expensive and difficult to use. In addition, MIMD machines are inefficient on fine-grained applications, which require frequent interaction among the processing elements (PEs). This paper surveys research efforts that seek to reduce the inefficiencies associated with managing control-parallelism on SIMD machines.1 These efforts are organized into three major categories: (1) advances made within the SIMD model; in particular, autonomous features allowing the PEs to locally modify the operation of some instructions, (2) architectures that have attempted to retain the advantages of the SIMD model, while enriching its control organization to allow better support of control-parallelism, and (3) the concurrent-interpretation model: a centralized-control model that shares the control unit at the instruction level (instead of the thread level, as per the SIMD model), allowing efficient support of control-parallelism on a centralized-control organization.

Progress in Internet Security

Abstract: This chapter surveys the state of security within the Internet protocol suite, including standard protocols and also widely used non-standard protocols. Key security technologies such as DNS Security, Secure Sockets Layer, and Internet key management are reviewed. Selected application and infrastructure technologies are reviewed, with both threats and security approaches being discussed. Some non-technical challenges to deploying a more secure Internet are also discussed. Progress made towards a more secure Internet during the past decade is highlighted throughout the chapter.

Formality in Specification and Modeling: Developments in Software Engineering Practice

Abstract: Formal methods have been a controversial subject among software engineering practitioners for twenty years However, advances in the technology supporting formal methods, coupled with a realistic view of their potential for commercial application, have brought about marked improvements in the ease with which formal techniques can be integrated into industrial software development This paper reviews the use of formal techniques for modeling systems in the commercial software development context The basic ideas of formality and formal methods are introduced The characteristics of formal models are introduced via a small example based on a commercial application Reports of experiences in applying formal techniques in industrial contexts lead to a discussion of the promises and challenges facing formal methods in industry today