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A new challenge is emerging due to the advent
of new classes of applications and technologies such as smart environments, sensor networks, mobile systems, peertopeer systems, cloud computing etc. In these settings, the underlying distributed systems cannot be fully managed but it needs some degree of self-management that depends on the specific application domain. However, it is possible
to delineate some common consequences of the presence of such self management: first, there is no entity that can always ensure the validity of the system assumptions during the entire computation and, second, no one knows
accurately who joins and who leaves the system at any
time introducing a kind of unpredictability in the system
composition (this phenomenon of arrival and departure
of processes in a system is also known as churn).
As a consequence, distributed computing abstractions have to deal not only with asynchrony and failures, but also with this dynamic dimension where a process that does not crash can leave the system at any time implying that membership can fully change several times during the same
computation. Hence, the abstractions for reliable distributed compiuting
have to be reconsidered
to take into account this new “adversary” setting. This selfdefined
and continuously evolving distributed system, that
we will name in the following dynamic distributed system,
makes abstractions more difficult to understand and master
than in distributed systems where the set of processes is
fixed and known by all participants. The churn notion
becomes thus a system parameter whose aim is to make
tractable systems having their composition evolving along
The presentation analyzes the issues in building a regula register in an environment that considers crashs and byzantine failures.
This presentation has been delivered during the Retirement Seminar for Professor Santosh Shrivastava that took place in Newcastle (UK) on september 2011.