Flexible Transactional Coordination in the Peer Model

The Peer Model is a model for the specification of coordination aspects found in concurrent and distributed systems. It provides modeling constructs for flows, time, remoting and exception handling. The main concepts of the ground model are peers, wirings, containers, entries and services. Its intent is to introduce specific modeling abstractions of concurrency and distribution to make designs more readable and suitable for larger problems. However, there still exist coordination aspects that are not straight forward to model with it. In this paper, therefore the Peer Model is extended by modeling constructs for nested, distributed transactions based on the Flex transaction model. This approach eases the advanced control of structured and distributed coordination scenarios that have to cope with complex, dependent and concurrent flows. The evaluation introduces a coordination challenge that requires adaptive and transactional distribution of resources, dependencies between concurrent activities, error handling and compensation. It demonstrates the improvements that can be achieved with the new modeling concepts.