The availability of data in a distributed database can be increased by replication, where a data object may have several copies residing on different sites. If data is replicated, it may still be available after failures. However, this increase in data availability may result in an increase in the cost of opertion execution. The research proposed herein seeks to develop methods that increase data availability at low costs. Futhermore, the mechanisms we explore allow the data to remain accessible in spite of site or communication failures, even when such failures lead to network partitioning. We propose to develop a new paradigm for fault tolerant concurrency control protocols. This paradigm furthers our understanding of such protocols, and provides us with new insights for the development of new protocols. We specifically proposed development protocols that allow the execution of read-only transactions and the efficient execution of transactions in databases with well defined information flow patterns. Finally, we propose to investigate methods for increasing the availability of abstract data objects where semantic information is available about the data objects in the databaase.
