This paper presents a meta protocol that allows the dynamic replacement of replication control protocols in replicated databases. The meta protocol is motivated by the diversity of concurrency control and replication control protocols that implement different transaction isolation levels. The replacement of protocols allows applications to dynamically adapt themselves to consistency and data access latency requirements. Such kind of adaptivity is important in mobile systems, where weaker consistency levels are acceptable when nodes are disconnected from a network, but stronger levels may be required when nodes are connected to each other. The paper defines three properties that meta protocol executions have to enforce and specifies a protocol that satisfies these properties. The protocol is based on a transaction execution model, uniform reliable broadcast and uniform consensus. Finally, we outline a dynamic adaptable architecture that is being implemented that includes the meta protocol and that makes use of an aspect oriented framework.

The construction of adaptive replicated systems, in which the replication control protocols can be replaced at runtime, requires to face with complex structural concerns that include: (i) the integration of replication control protocols with the application code, (ii) the the interchangeability of protocol variants, (iii) the observation and handling of events in a distributed system, and (iv) the consistency of the replication control mechanism. In this paper, we show a way to tackle that complexity with the help of Design Patterns and Aspect Oriented Programming (AOP).