Flexible modeling of policy-driven upstream notification strategies

We present the advantages of a new coordination model termed "Peer Model" for the design of coordination strategies and introduce new extensions for the modeling of time and reference. The motivating example is the wireless, reliable, and timely upstream propagation of events about approaching trains, detected by sensors, to a rail crossing. Embedded wireless nodes along the tracks propagate the events upstream. The Peer Model provides flexibility, as new requirements do not demand a complete re-design and reimplementation of notification strategies, which is achieved by means of high-level abstractions, modularization, and patterns with exchangeable policies.