Visibility in Event-Based Systems
Ludger Fiege · Technischen Universität Darmstadt · 2008
Events are of increasing importance in modern distributed systems. Growing interconnectivity and continuous evolution demand a loose coupling of communicating parties that traditional paradigms like request/reply can hardly provide. The event-based computing paradigm offers the required flexibility, but existing work has neglected problems of system engineering and management. Today's event-based systems mostly rely on flat design spaces and they are unstructured. Notification services convey data by matching it with issued subscriptions, not distinguishing subsets within the complete set of consumers. This results in a growing complexity that is hard to control, raising security, management, engineering, and scalability issues. This thesis presents a scoping concept for event-based systems. Scopes reify system structure and hierarchically arrange groups of producers, consumers, and other scopes in directed acyclic graphs. They limit the visibility of notifications and govern their distribution within this structure. Scopes provide both a design-time tool and an implementation framework that addresses the aforementioned problems; they control side effects, decompose the system, and allow for adaption and management of its parts.