The most certain and effectual check upon errors which arise in the
process of computation, is to cause the same computations to be made
by separate and independent computers; and this check is rendered still
more decisive if they make their computations by different methods.
— Dr. Dionysius Lardner ”Babbages’s calculating engine” in the Edinburgh Review, 1834.
There is a rising dependency in the society on computer systems and the services they provide. This dependency imposes still higher demands to the dependability of the systems. Dependability is a concept that considers every cross-cutting concerns, that poses a potential threat to the level of service provided by the system. Due to the framing of our research, a natural place to start investigating dependable software architectures for pervasive computing, is to look at the existing infrastructure designs currently employed in distributed systems.
The architecture of at collaborative system, determines the nature of the components of the system and the placement of these components on the computers of the various users participating in a collaborative session. Archetypical architectural patterns are the centralized, the replicated, the client-server, and the peer-to-peer architectures.