The view holder approach: Utilizing customized materialized views to create database services suitable for mobile database applications.

摘要

Mobile computing allows a user utilizing a mobile computer such as PDAS, Au-toPCs, and notebooks, to access other computers regardless of the location of the user or the time of day. However, conditions in a mobile environment change rapidly and dramatically, and every component of the environment must be able to respond to unpredictable changes in bandwidth, power consumption, and other resources affecting the work being performed by a mobile user. Data shipping, both caching and hoarding, provide the only means to support disconnected mobile operations. In the context of mobile client-server database applications, data cached can take the form of a materialized view. Personalization of information gathering for mobile clients is becoming increasingly important due to the computing, communication, and storage differences among mobile devices (i.e., a laptop vs. a pager) and the amount of information available from today's database environments and the Internet.; To this end, this dissertation presents the development of customizable view maintenance services, called the View Holder approach, whose middleware mechanism within the fixed network dynamically maintains versions of the views so that to meet the data consistency and currency requirements of a particular mobile client. In a general form, a View Holder can support a community of mobile clients with common interests. The motivation for maintaining versions is to compensate for the data changes that occurred to the materialized views that were used during disconnection as well as to reduce the cost of wireless communication. In order to maintain these views, customized view maintenance is performed at the data sources by translating the mobile machine's request into a materialization program containing a triggering constraint or monitoring routine. A materialization program is created to take advantage of the latest mobile agent technology. Mobile agents are autonomous programs that migrate from one machine to another within a network on behalf of a client and can perform tasks on any machine that provides agent hosting capabilities. Mobile agents are ideal for mobile computing environments due to their ability to support asynchronous communication and flexible query processing since tasks can be delegated to mobile agents when a mobile client is disconnected.; Every view maintenance strategy and their associated levels of view consistency give a mobile client a variety of personalized view maintenance options for reducing the client's dependency on fixed network resources, thus offering a finer grain of control and balance between data availability, the amount of wireless communication, and the expense of maintaining consistency guarantees. A fine grained approach to creating and managing materialized views lets the mobile environment take advantage of the strengths of the fixed network in order to adapt to adverse wireless conditions and to extend the usability of mobile devices while enhancing personal productivity.