Intersecting sets:: a basic abstraction for asynchronous agreement problems

Defining good abstractions is a central issue when one wants to understand the deep structure and basic principles that underlie computing mechanisms. This paper introduces a basic and particularly simple distributed computing abstraction suited to asynchronous distributed agreement problems. This abstraction, called Intersecting Sets, requires each process to deposit a value and allows each non-faulty process to obtain a subset of these values such that any two such sets have a non-empty intersection. This simple abstraction captures an essential part of distributed agreement problems. After having introduced and motivated this abstraction, the paper investigates its properties, its power and its benefit when solving distributed agreement problems.