DREAM: Distributed Reliable Event-Based Application Management

New applications and the convergence of technologies, ranging from sensor networks to ubiquitous computing and from autonomic systems to eventdriven supply chain management, require new middleware platforms that support proactive event notification. We present a system overview and discuss the principles of Dream, a reactive middleware platform that integrates event detection and composition mechanisms in a highly distributed environment; fault-tolerant and scalable event notification that exploits a variety of filter placement strategies; content-based notification to formulate powerful filters and concept-based notification to extend content-based filtering to heterogeneous environments; middleware-mediated transactions that integrate notifications and transactions; and scopes, which are administration primitives for both deploymentand runtime configurability, as well as for the management of policies. We discuss four prototypes that were implemented as proof of concept systems and present lessons learned from them.