Users of mobile computers, such as palmtops, notebook computers and personal communications systems, will soon have online access to a large number of databases via wireless networks. The potential market for this activity is estimated to be billion of dollars annually, in access and communication charge. For example, while on the road, passengers will access airline and other carriers schedules, and weather information. Investors will access prices of financial instruments, salespeople will access inventory data, callers will access traffic information, and wearable ubiquitous computers will access a wide variety of databases. Wireless communication is more expensive and less reliable that wire communication. We demonstrate that the way online data is allocated/replicated at mobile computers affect both, cost and data availability, and therefore data allocations has to change according to changing conditions, such as access patterns, users' location, etc. Presently, the allocation scheme of a distributed database is established in a static fashion, when the database is designed. The allocation scheme remains fixed until the designer manually intervenes to change the number of replicas or their location. We show that this is an unsatisfactory solution, particularly in mobile computing.
