Abstract
This paper presents a novel adaptation mechanism that allows every node of a gossip-based broadcast algorithm to adjust the rate of message emission 1) to the amount of resources available to the nodes within the same broadcast group and 2) to the global level of congestion in the system. The adaptation mechanism can be applied to all gossip-based broadcast algorithms we know of and makes their use more realistic in practical situations where nodes have limited resources whose quantity changes dynamically with time without decreasing the reliability.

Abstract
This paper introduces a calculus of state-based software components modelled as concrete coalgebras for some Set endofunctors, with specified initial conditions. The calculus is parametrized by a notion of behaviour, introduced as a strong ( usually commutative) monad. The proposed component model and calculus are illustrated through the characterisation of a particular class of components, classified as separable, which includes the ones arising in the so-called model oriented approach to systems' design.

Abstract
Although the principles behind generic programming are already well understood, this style of programming is not widespread and examples of applications are rarely found in the literature. This paper addresses this shortage by presenting a new method, based on generic programming, to automatically visualize recursion trees of functions written in Haskell. Crucial to our solution is the fact that almost any function definition can be automatically factorized into the composition of a fold after an unfold of some intermediate data structure that models its recursion tree. By combining this technique with an existing tool for graphical debugging, and by extensively using Generic Haskell, we achieve a rather concise and elegant solution to this problem. © 2003 Published by Elsevier Science B.V.

Abstract
In this article we propose a role based model for the specification of organized collective agency, based on the legal concept of artificial person and on the normative perspective of organizational systems. We focus on the analysis of groups of agents ( humans or not) that want to act collectively in a ( more or less) permanent basis, and in a stable and organized way, as it is the typical case of organizations. We argue that in those cases such groups of agents should give rise to a new agent, that we call of institutionalized agent, with its own identity, whose structure is essentially defined through the characterization of a set of roles and whose behavior is determined by the acts of the agents that play such roles. We also present a deontic and action modal logic that captures the concept of acting in a role and relates it with the deontic notions of obligation, permission and prohibition. This logic is used in the formal specification of institutionalized agents and of societies of agents and in the rigorous analysis of them. We pay particular attention to the interaction between agents through contracts or other normative relations. A high level specification language is also suggested.

Abstract
View Synchrony (VS) is a powerful abstraction in the design and implementation of dependable distributed systems. By ensuring that processes deliver the same set of messages in each view, it allows them to maintain consistency across membership changes. However, experience indicates that it is hard to combine strong reliability guarantees as offered by VS with stable high performance. In this paper we propose a novel abstraction, Semantic View Synchrony (SVS), that exploits the application's semantics to cope with high throughput applications. This is achieved by allowing some messages to be dropped while still preserving consistency when new views are installed. Thus, SVS inherits the elegance of view synchronous communication. The paper describes how SVS can be implemented and illustrates its usefulness in the context of distributed multi-player games.

Abstract
Total order multicast greatly simplifies the implementation of fault-tolerant services using the replicated state machine approach. The additional latency of total ordering can be masked by taking advantage of spontaneous ordering observed in LANs: A tentative delivery allows the application to proceed in parallel with the ordering protocol. The effectiveness of the technique rests on the optimistic assumption that a large share of correctly ordered tentative deliveries offsets the cost of undoing the effect of mistakes. This paper proposes a simple technique which enables the usage of optimistic delivery also in WANs with much larger transmission delays where the optimistic assumption does not normally hold. Our proposal exploits local clocks and the stability of network delays to reduce the mistakes in the ordering of tentative deliveries. An experimental evaluation of a modified sequencer-based protocol is presented, illustrating the usefulness of the approach in fault-tolerant database management.