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This paper uses a theory of composition based on existential and universal properties. Universal properties are useful to describe components interactions through shared variables. However, some universal properties do not appear directly in components speci cations and they must be constructed to prove the composed system. Coming up with such u n iversal properties often requires creativity. The paper shows through two examples how this construction can be achieved. The principle used is rst presented with a toy example and then applied to a more substantial problem.

Abstract. We are investigating a component-based approach for formal design of distributed systems. In this paper, we introduce the framework we use for specification, composition and communication and we apply it to an example that highlights the different aspects of a compositional design, including top-down and bottom-up phases, proofs of composition, refinement proofs, proofs of program texts, and component reuse.

This paper proposes a methodology for designing a class of algorithms for computing functions in dynamic distributed systems in which communication channels and processes may cease functioning temporarily or permanently. Communication and computing may be interrupted by an adversary or by environmental factors such as noise and power loss. The set of processes may be partitioned into subsets that cannot communicate with each other; algorithms in which all such subsets behave in a similar fashion, regardless of size and identities of processes, are called self-similar algorithms. Algorithms adapt to changing conditions, speeding up or slowing down depending on the resources available. The paper presents necessary and sufficient conditions for the application of a self-similar strategy. Self-similar algorithms are developed for several problems by applying the methodology.