A Peer-to-Peer Approach to Content-Based Publish/Subscribe

Publish/subscribe systems are successfully used to decouple distributed applications. However, their e#ciency is closely tied to the topology of the underlying network, the design of which has been neglected. Peer-to-peer network topologies can o#er inherently bounded delivery depth, load sharing, and self-organisation. In this paper, we present a contentbased publish/subscribe system routed over a peer-to-peer topology graph. The implications of combining these approaches are explored and a particular implementation using elements from Rebeca and Chord is proven correct

Visibility in Event-Based Systems

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

Mobility Support with REBECA

Publish/subscribe (pub/sub) proliferates loose coupling and is touted to facilitate mobility. The inherent loose coupling even allows existing applications to be transferred to mobile environments, if an appropriate infrastructure support is available. However, existing pub/sub middleware are mostly optimized for static systems where users as well as the underlying system structure is rather fixed. In this paper, we analyze the necessary steps to support mobile clients with publish/subscribe middleware. The REBECA content-based pub/sub service is extended to accommodate to physically mobile clients, offering a location transparent access to the middleware without degrading the previously guaranteed quality of service. The transparent access allows existing applications to be seamlessly transferred from a static to a mobile scenario without having to adapt client applications