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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.

Shared tuple spaces serve as coordination medium for independent processes to exchange data and messages in a flexible way. If communication takes place over the Internet, security becomes an important issue. It must be forbidden that unauthorized processes get access to protected data. In this paper, we present an authorization model for a space-based middleware that uses its own coordination mechanisms for defining fine-grained access control policies. By integrating coordination and security mechanisms into one single concept, the model allows for flexible and secure distributed collaboration.

Semantic technologies promise to solve challenging problems of current enterprise information systems, e.g., the integration of heterogeneous information clients and the evaluation of complex data dependencies. As many of these problems also apply to coordination applications, recent research initiatives have proposed to integrate coordination models with semantic technology. In this paper, we present such an integrated coordination model which combines logic-based reasoning with a reliable semantic subscription mechanism. We present a formal definition of the model's behavioral semantics and investigate the added value of using semantic technologies. Finally, we draw first conclusions about the practical applicability of the proposed approach based on performance benchmarks of a prototype implementation.