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Automation systems play an important role in the economy of most industrialized countries. One prominent feature of such systems relates to dependability, as unexpected crashes can both put human-life in danger and cause massive money looses. The first Latin-American Workshop on Dependable Automation Systems (WDAS) aims to provide an opportunity for researchers and industrial partners to discuss problems related to the development of safe-critical automation systems.

Although there is a large body of research in dependability, architectural level reasoning about dependability is only just emerging as an important theme in software development. This is due to the fact that dependability concerns are often left until too late in the process of development. In addition, the complexity of emerging applications and the trend of building trustworthy systems from existing untrustworthy components are urging dependability concerns to be considered at the architectural level.

Devising wait-free resilient implementations of concurrent objects from fault-prone base objects is a fundamental challenge of computer science. Wait-free means that any process that invokes an operation eventually receives a reply after executing a finite number of its own steps, even if other processes are arbitrarily slow or even failed. Resilience means that the implementation of the concurrent object behaves correctly despite the failure of up to t base objects (t being a threshold parameter a priori defined). The tutorial surveys different techniques to build wait-free resilient implementations of concurrent objects. Three complementary classes of techniques are presented: (1) fault-tolerance “by replication”, (2) fault-tolerance “by diversity”, and (3) fault-tolerance “by oracle”, respectively. The first is the well-known redundancy technique and its applicability depends on the kinds of faults that the objects can suffer. The second consists in combining the base objects with objects of other types (type refers here to a programming language notion: the type has to be powerful enough to allow implementing resilient objects). This technique basically relies on the universality of consensus objects. The third technique relies on the information we can obtain about the operational status of the processes.

Agreement protocols are fundamental for the design of dependable systems. They ensure consistent cooperation among distributed entities, helping both to keep the continuity of services in spite of failures and to enhance performance. Consensus is the greatest common denominator among all agreement problems. It allows a set of processes to agree on a common output value. Theoretical advances have been reached, thanks to the consensus problem solutions through the use of unreliable failure detectors, which have been proved to be essential in solving many other agreement problems in environments with temporal uncertainties. Such advances have been exploited in order to (i) find efficient solutions to agreement problems, (ii) identify minimal synchronous conditions for their solution and (iii) characterize more precisely their behavior (blocking or progression) in presence of network disturbs. From a software engineering view point, consensus-based protocols give rise to simple and modular solutions. Basic components () are identified in order to construct richer ones (). These components are in turn the fundamental pieces of middleware for reliable distributed programming.