Table Of ContentDATA 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
