Concurrent Computing with Shared Replicated Memory.

Any concurrent system can be captured by a concurrent Abstract State Machine (cASM). This remains valid, if different agents can only interact via messages. It even permits a strict separation between memory managing agents and other agents that can only access the shared memory by sending query and update requests. This paper is dedicated to an investigation of replicated data that is maintained by a memory management subsystem, where the replication neither appears in the requests nor in the corresponding answers. We specify the behaviour of a concurrent system with such memory management using concurrent communicating ASMs (ccASMs), provide several refinements addressing different replication policies and internal messaging between data centres, and analyse their effects on the runs with respect to consistency. We show that on a concrete level even a weak form of consistency is only possible, if view serialisability can be guaranteed.