Database Caching Over the Air-Storage

Previous research on broadcast databases in a mobile computing environment utilizing wireless channels has been focused on mechanisms for a mobile client to selectively pick database items in which the client is interested from a broadcast channel. The fundamental issue of identifying the appropriate database items for broadcast or refrained from being broadcast have largely been ignored. In this paper, we consider the concept of `air-storage', by treating the wireless broadcast media as a layer of cache storage. Broadcasting database items over the air-storage becomes similar in spirit to the caching of database items from the database server. Similarly, determining which database items need to be broadcast or refrained from being broadcast becomes similar in nature to cache management. Existing caching mechanisms are reviewed and management issues speci"c to the new air-storage are raised and discussed. In view of new issues in air-storage management, we propose and investigate several mechanisms in selecting the proper database items to be placed over this new layer of air-storage under a variety of data access patterns. Finally, the effectiveness of the mechanisms is evaluated by means of simulated experiments and the results are discussed.