Data Management for Mobile Computing PDF
Preview Data Management for Mobile Computing
DATA MANAGEMENT FOR MOBILE COMPUTING The Kluwer International Series on ADVANCES IN DATABASE SYSTEMS Series Editor Ahmed K. Elmagarmid Purdue University West Lafayette, IN 47907 Other books in the Series: DATABASE CONCURRENCY CONTROL: Methods, Performance, and Analysis by Alexander Thomasian ISBN: 0-7923-974 I-X TIME-CONSTRAINED TRANSACTION MANAGEMENT Real-Time Constraints in Database Transaction Systems by Nandit R. Soparkar, Henry F. Korth, Abraham Silberschatz ISBN: 0-7923-9752-5 SEARCHING MULTIMEDIA DATABASES BY CONTENT by Christos Faloutsos ISBN: 0-7923-9777-0 REPLICATION TECHNIQUES IN DISTRIBUTED SYSTEMS by Abdelsalam A. Helal, Abdelsalam A. Heddaya, Bharat B. Bhargava ISBN: 0-7923-9800-9 VIDEO DATABASE SYSTEMS: Issues, Products, and Applications by Ahmed K. Elmagarmid, Haitao Jiang, Abdelsalam A. Helal, Anupam Joshi, Magdy Ahmed ISBN: 0-7923-9872-6 DATABASE ISSUES IN GEOGRAPHIC INFORMATION SYSTEMS by Nabil R. Adam and Aryya Gangopadhyay ISBN: 0-7923-9924-2 INDEX DATA STRUCTURES IN OBJECT-ORIENTED DATABASES by Thomas A. Mueck and Martin L. Polaschek ISBN: 0-7923-9971-4 INDEXING TECHNIQUES FOR ADV ANCED DATABASE SYSTEMS by Elisa Bertino, Beng Chin Ooi, Ron Sacks-Davis, Kian-Lee Tan, Justin Zobel, Boris Shidlovsky and Barbara Catania ISBN: 0-7923-9985-4 MINING VERY LARGE DATABASES WITH PARALLEL PROCESSING by Alex A. Freitas and Simon H. Lavington ISBN: 0-7923-8048-7 DATA MANAGEMENT FOR MOBILE COMPUTING by Evaggelia Pitoura University of/ oannina /oannina, Greece and George Samaras University of Cyprus Nicosia, Cyprus SPRINGER SCIENCE+BUSINESS MEDIA, LLC ISBN 978-1-4613-7526-5 ISBN 978-1-4615-5527-8 (eBook) DOI 10.1007/978-1-4615-5527-8 Library of Congress Cataloging-in-Publication Data A C.I.P. Catalogue record for this book is available from the Library of Congress. The publisher offers discounts on this book when ordered in buJk quantities. For more information contact: Sales Department, Kluwer Academic Publishers, 101 Philip Drive, Assinippi Park, Norwell, MA 02061 Copyright © 1998 by Springer Science+Business Media New York Originally published by Kluwer Academic Publishers in 1998 Softcover reprint ofthe hardcover Ist edition 1998 AII rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, mechanical, photo copying, recording, or otherwise, without the prior written permission of the publisher, Springer Science+Business Media, LLC. Printed on acid-free pap er. CONTENTS PREFACE vii 1 INTRODUCTION 1 1.1 Wireless Technologies 2 1.2 Wireless Architecture 6 1.3 Applications 9 1.4 Issues and Limitations 11 2 SOFTWARE ARCHITECTURES 15 2.1 Mobile Computing Models 16 2.2 Environmental Awareness 25 2.3 An Example: Web Browsing 29 3 SYSTEM-LEVEL SUPPORT 37 3.1 Disconnected Operation 37 3.2 Weak Connectivity 48 3.3 Mobility 61 3.4 Failure Recovery 64 4 INFORMATION MANAGEMENT 71 4.1 Broadcast 71 4.2 Caching and Broadcast 77 4.3 Querying Location Data 83 4.4 Other Topics 84 5 LOCATION MANAGEMENT 87 5.1 The Location Problem 87 v VI DATA MANAGEMENT FOR MOBILE COMPUTING 5.2 Two-tier Schemes 89 5.3 Hierarchical Schemes 95 5.4 Evaluating Performance 106 5.5 Concurrency and Recovery 107 6 CASE STUDIES 111 6.1 Rover 111 6.2 Bayou 115 6.3 Coda 118 6.4 WebExpress 122 7 CONCL USIONS 127 REFERENCES 137 INDEX 153 PREFACE Earth date, August 11, 1997 "Beam me up Scottie!" "We cannot do it! This is not Star Trek's Enterprise. This is early years Earth." True, this is not yet the era of Star Trek, we cannot beam captain James T. Kirk or captain Jean Luc Pickard or an apple or anything else anywhere. What we can do though is beam information about Kirk or Pickard or an apple or an insurance agent. We can beam a record of a patient, the status of an engine, a weather report. We can beam this information anywhere, to mobile workers, to field engineers, to a track loading apples, to ships crossing the Oceans, to web surfers. We have reached a point where the promise of information access anywhere and anytime is close to realization. The enabling technology, wireless networks, exists; what remains to be achieved is providing the infrastructure and the software to support the promise. Universal access and management of information has been one of the driving forces in the evolution of computer technology. Central computing gave the ability to perform large and complex computations and advanced information manipulation. Advances in networking connected computers together and led to distributed computing. Web technology and the Internet went even further to provide hyper-linked information access and global computing. However, restricting access stations to physical location limits the boundary of the vision. The real global network can be achieved only via the ability to compute and access information from anywhere and anytime. This is the fundamental wish that motivates mobile computing. vii viii DATA MANAGEMENT FOR MOBILE COMPUTING This evolution is the cumulative result of both hardware and software advances at various levels motivated by tangible application needs. Infrastructure re search OIl communications and networking is essential for realizing wireless sys tems. Equally important is the design and implementation of data management applications for these systems, a. task directly affected by the characteristics of the wireless medium and the resulting mobility of data resources and compu tation. Although being a relatively new area, mobile data management has provoked a proliferation of research efforts motivated by both a great market potential and by many challenging research problems. The focus of this book is on the impact of mobile computing on data manage ment beyond the networking level. The purpose is to provide a thorough and cohesive overview of recent advances in wireless and mobile data management. The book is written with a critical attitude. We probe the new issues intro duced by wireless and mobile access to data and what are both their conceptual and practical consequences. The book provides a single source for researchers and practitioners who want to keep current on the latest innovations in the field. It can also serve as a textbook for an advanced course on mobile computing or as a companion text for a variety of courses including courses on distributed systems (Chapters 1-6), database management (Chapters 2-6), transaction management (Chap ters 3,6), operating or file systems (Chapters 2-3, 6), information retrieval or dissemination (Chapter 4), and web computing (Chapter 2-3, 6). ORGANIZATION OF THE BOOK The introductory chapter, Chapter 1, provides background material. It starts by reviewing a wide spectrum of wireless technologies by placing special em phasis on their characteristics that affect data management. Then, we present the underlying architecture, basic definitions and concepts, and a number of applications that take advantage of mobile computing. The chapter concludes by enumerating the basic challenges in mobile data management. Chapter 2 presents the general principles behind building software for mobile applications. Software architectures ranging from client-servers and proxies to software mobile agents are introduced. Structuring distributed applications by efficiently partitioning the computation between mobile and static components is also discussed. Concepts such as application-awareness of location and dis connection, and adaptation to varying connectivity conditions are introduced. Preface IX At the end of this chapter, a concrete realization of these architectures and concepts is provided through their deployment in the design of an example web-browsing application. Chapter 3 concentrates on support provided at the system level. Techniques for sustaining frequent network disconnections and weak connectivity are discussed within the context of file, database management, workflow management, object based, and web systems. Such techniques include revising cache management methods, replication protocols, and transaction models. Then, treating mobil ity by relocating data and computation is covered. Finally, failure recovery is discussed with special emphasis on distributed checkpointing. Chapter 4 is devoted to information representation, dissemination and man agement. The deployment of broadcast for disseminating information is the first topic discussed. Methods for organizing broadcast data, approaches to combining on-demand and broadcast data delivery, techniques for cache man agement in broadcast-based systems and mechanisms for invalidating caches through broadcast are reviewed. Thi chapter also presents data models and query management techniques for location data as well as an overview of other novel topics in query management. Chapter 5 is dedicated to methods for location management. Various schemes for the distribution of databases containing users' locations as well as techniques for handling location updates and queries are presented. Techniques such as caching and replication of the location of those users that are frequently looked up can reduce the location query cost with an increase in the update cost. Partial updates and partitioning techniques can reduce the cost of updates. Concurrency and failure handling for location databases is also covered. Chapter 6 is devoted to presenting case studies. We discuss how the issues presented in the previous chapters have been addressed in the following systems: the CMU's Coda file system, the MIT's Rover application toolkit, the Xerox's Bayou weak replication storage system and IBM's WebExpress web browsing system. The book concludes by summarizing problems and solutions, and suggesting promising research topics. 1 INTRODUCTION Wireless communications permit users carrying portable computers to retain their network connection even when mobile. The resulting computing paradigm is called mobile or nomadic computing. In conjunction with the existing com puting infrastructure, mobile computing adds a new dimension to distributed computation that of universal access to information anytime and anyplace. This dimension enables a new class of applications. However, the realization of these applications presupposes that a number of challenges regarding data management are met. Data management for distributed computing has spawned a variety of research work and commercial products. New computational models, algorithms, mea surements of efficiency, systems, and applications have been and are being explored. At the present time, building software systems for mobile computing seems to be an even more stimulating task for at least two reasons. First, the parameters that must be taken into account are not yet clearly understood and defined. Then, the challenges that must be met are enormous: variability in bandwidth availability, frequent network disconnections, mobility of data and computation, large scale both in the distribution and in the number of compu tational elements. In a sense, mobile computing is the worst case of distributed computing since fundamental assumptions about connectivity, immobility and scale are no longer valid. This chapter introduces basic concepts and issues pertaining to mobile com puting. The remainder of the chapter includes a short survey of the underlying wireless technologies, background definitions and example applications. The chapter concludes by identifying issues and limitations introduced by mobile computing. 1 E. Pitoura et al., Data Management for Mobile Computing © Kluwer Academic Publishers 1998
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