Data replication is useful in a database system for two reasons. It can improve the performance and increase the reliability of information. By accessing the copy in the nearest site, expensive remote access can be avoided. By storing critical data at multiple locations, the data may still be available even if some machines are down. Availability and consistency are competing goals in the management of replicated data. It is desirable to have a high data availability while the database is still consistent in users' view. On the other hand, correct schemes that provide high availability may suffer performance penalties. Thus, when designing a replica management protocol, it is important to take all these three aspects into account. My research interests in this area include the design of efficient replica control protocol that can provide high data availability and some related theoretical aspects.