Section: New Results

Parameterized Communicating Automata

As a part of our research program on concurrent systems with variable communication topology, we studied system models where the topology is static but unknown, so that it becomes a parameter of the system. In [28] , we introduced parameterized communicating automata (PCAs), where finite-state processes exchange messages via rendez-vous or through bounded FIFO channels. Unlike classical communicating automata, a given PCA can be run on any network topology of bounded degree. We presented various Büchi-Elgot-Trakhtenbrot theorems for PCAs, which roughly read as follows: Let $\varphi$ be an existential MSO formula and $T$ be any of the following topology classes: pipelines, ranked trees, grids, or rings. There is a PCA that is equivalent to $\varphi$ on all topologies from $T$. In the case where each process executes a bounded number of contexts (each context restricting communication in a suitable way), we could show that PCAs are closed under complementation, are expressively equivalent to full MSO logic [29] , and have a decidable emptiness problem [31] . The papers [29] , [31] are a result of a collaboration with Akshay Kumar (IIT Kanpur) and Jana Schubert (TU Dresden).