Numerous systems for dissemination, retrieval, and archiving of documents have been developed in the past. Those systems often focus on one of these aspects and are hard to extend and combine. Typically, the transmission protocols, query and filtering languages are fixed as well as the interfaces to other systems. We rather envisage the seamless establishment of networks among the providers, repositories and consumers of information, supporting information retrieval and dissemination while being highly interoperable and extensible. We propose a framework with a single event-based mechanism that unifies document storage, retrieval, and dissemination. This framework offers complete openness with respect to document and metadata formats, transmission protocols, and filtering mechanisms. It specifies a high-level building kit, by which arbitrary processors for document streams can be incorporated to support the retrieval, transformation, aggregation and disaggregation of documents. Using the same kit, interfaces for different transmission protocols can be added easily to enable the communication with various information sources and information consumers.
@cite_12 is a push-model publish subscribe system for alerting within a wide-area network. It offers scalability by distributing filters over servers within the network and saving bandwidth by filtering close to the event sources and bundling similar subscriptions. Siena is modular and offers sophisticated filtering mechanisms including dynamic configuration and distribution. It lacks openness, document stream transformation, and scheduling.
@cite_12
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The components of a loosely coupled system are typically designed to operate by generating and responding to asynchronous events. An event notification service is an application-independent infrastructure that supports the construction of event-based systems, whereby generators of events publish event notifications to the infrastructure and consumers of events subscribe with the infrastructure to receive relevant notifications. The two primary services that should be provided to components by the infrastructure are notification selection (i.e., determining which notifications match which subscriptions) and notification delivery (i.e., routing matching notifications from publishers to subscribers). Numerous event notification services have been developed for local-area networks, generally based on a centralized server to select and deliver event notifications. Therefore, they suffer from an inherent inability to scale to wide-area networks, such as the Internet, where the number and physical distribution of the service’s clients can quickly overwhelm a centralized solution. The critical challenge in the setting of a wide-area network is to maximize the expressiveness in the selection mechanism without sacrificing scalability in the delivery mechanism. This paper presents SIENA, an event notification service that we have designed and implemented to exhibit both expressiveness and scalability. We describe the service’s interface to applications, the algorithms used by networks of servers to select and deliver event notifications, and the strategies used