AMECOS: A Modular Event-based Framework for Concurrent Object Specification

In this work, we introduce a modular framework for specifying distributed systems that we call AMECOS. Specifically, our framework departs from the traditional use of sequential specification, which presents limitations both on the specification expressiveness and implementation efficiency of inherently concurrent objects, as documented by Casta{~n}eda, Rajsbaum and Raynal in CACM 2023. Our framework focuses on the interface between the various system components specified as concurrent objects. Interactions are described with sequences of object events. This provides a modular way of specifying distributed systems and separates legality (object semantics) from other issues, such as consistency. We demonstrate the usability of our framework by (i) specifying various well-known concurrent objects, such as shared memory, asynchronous message-passing, and reliable broadcast, (ii) providing hierarchies of ordering semantics (namely, consistency hierarchy, memory hierarchy, and reliable broadcast hierarchy), and (iii) presenting novel axiomatic proofs of the impossibility of the well-known Consensus and wait-free Set Agreement problems.