Guest editorial: special section on data management systems and mobile computing

Abstract

THE need for “information anywhere anytime” has been a driving force for the increasing growth in Web and Internet technology, wireless communication, and portable computing devices. Mobile computing is the merger of recent advances in computing and communication technologies with the aim of providing a seamless and ubiquitous computing environment to mobile users. In such mobile environments, database applications are enhanced with useful features of wireless technology. For example, users are allowed to establish a mobile office where they can communicate with other users (mobile or stationary), access information from various sources, and manage their work while staying mobile. This feature is important for enabling of mobile workforces supporting ubiquitous services such as weather and forecasting services, financial market reporting, yellow pages, road maps and directions, telematics, point-of-sale applications, in-field work dispatch, law enforcement, military, and the like. By nature, mobile computing environments are characterized by severe resource constraints and unstable operating conditions; this adds a new dimension to the technical challenges for database systems and management. Many software problems associated with data management, transaction management, and data recovery have their origin in distributed database systems. In mobile computing, however, these problems become more difficult to solve, mainly because of the narrow bandwidth of the wireless communication channels, the relatively short active life of the power supply of mobile units, and the changing locations of required information (sometimes in cache, sometimes in air, sometimes at the server). Further, in many mobile database applications, data changes very rapidly (or even constantly). Users need to receive timely information in order to make critical decisions (e.g., stock market information and trading). Thus, response time becomes a much more key performance metric. In addition to the traditional response time, the active life of the user’s battery is also an important performance merit. Wireless networks differ from wired networks in many ways. Database users over a wired network remain connected not only to the network but also to a continuous power source. In a wireless network, however, both the response time and the active life of the user’s battery are important. In order to conserve energy and extend battery life, clients can slip into doze mode. Clients can be awakened from the doze mode when the server needs to communicate with the client. Mobile applications can be categorized as 1) vertical applications and 2) horizontal application. In vertical applications, users access data within a specific cell and access is denied to users outside of that cell. For example, users can obtain information on the location of doctors or emergency centers within a cell or parking availability data at an airport cell. In horizontal applications, users cooperate on accomplishing a task and they can handle data distributed throughout the system. The market for horizontal applications is growing; two types of applications that fall in this category are mail-enabled applications and information services to mobile users. These two types of applications differ in the type of data they manage. Public data is primarily managed by vertical applications, while shared data is used by horizontal applications, possibly with some replication. Copies of shared data may be stored both in base and mobile stations. This presents a variety of difficult problems in transaction management consistency, as well as in the integrity and scalability of the architecture. Data management is concerned with the modeling, efficient storage, retrieval, and manipulation of information. From a data management standpoint, mobility of the clients/nodes provides an interesting variation to distributed computing. Mobile databases can be distributed under two possible scenarios: 1) The entire database is distributed mainly among the wired components, possibly with full or partial replication. A base station manages its own database with a DBMS-like functionality, with additional functionality for locating mobile units and additional query and transaction management features to meet the requirements of mobile environments. 2) The database is distributed among wired and wireless components. Data management responsibility is shared among base stations and mobile units. In this environment, traditional distributed database techniques may not work. These different ways of managing data in mobile environments entail additional considerations and variation with regard to distributed database management. IEEE TRANSACTIONS ON COMPUTERS, VOL. 51, NO. 10, OCTOBER 2002 1121