The behavioural theory of concurrent systems states that any concurrent
system can be captured by a behaviourally equivalent concurrent Abstract State
Machine (cASM). While the theory in general assumes shared locations, it
remains valid, if different agents can only interact via messages, i.e. sharing
is restricted to mailboxes. There may even be a strict separation between
memory managing agents and other agents that can only access the shared memory
by sending query and update requests to the memory agents. This article is
dedicated to an investigation of replicated data that is maintained by a memory
management subsystem, whereas the replication neither appears in the requests
nor in the corresponding answers. We show how the behaviour of a concurrent
system with such a memory management can be specified using concurrent
communicating ASMs. We provide several refinements of a high-level ground model
addressing different replication policies and internal messaging between data
centres. For all these refinements we analyse their effects on the runs such
that decisions concerning the degree of consistency can be consciously made.Comment: 23 page
