The JEDI event-based infrastructure and its application to the developmentof the OPSSWFMS

The development of complex distributed systems demands for the creation of suitable architectural styles (or paradigms) and related runtime infrastruc tures. An emerging style that is receiving increasing attention is based on the notion of event. In an event-based architecture, distributed software components interact by generating and consuming events. An event is the occ urrence of some state change in a component of a software system, made visi ble to the external world. The occurrence of an event in a component is asy nchronously notified to any other component that has declared some interest in it. This paradigm (usually called "publish/subscribe," from the names o f the two basic operations that regulate the communication) holds the promi se of supporting a flexible and effective interaction among highly reconfig urable, distributed software components. In the past two years, we have dev eloped an object-oriented infrastructure called JEDI (Java Event-Based Dist ributed Infrastructure). JEDI supports the development and operation of eve nt-based systems and has been used to implement a significant example of di stributed system, namely, the OPSS workflow management system (WFMS). The p aper illustrates the main features of JEDI and how we have used them to imp lement OPSS. Moreover, the paper provides an initial evaluation of our expe riences in using the event-based architectural style and a classification o f some of the event-based infrastructures presented in the literature.