"Siena is a research project aimed at designing and constructing a generic scalable publish/subscribe event-notification service."

"The technical basis of Siena is an innovatiove type of network service called content-based networking."

"The asynchrony, heterogeneity, and inherent loose coupling that characterize applications in a wide-area network promote event interaction as a natural design abstraction for a growing class of software systems. An emerging building block for such systems is an infrastruvture called publish/subscribe event notification service."

"We envision a ubiquitous event notification service accessible from every site on a wide-area network and suitable for supporting highly distributed applications requiring component interactions ranging in granualrity from fine to coarse.'

"Given that the primary purpose of an event notification service is to support notification selection and delivery, the challenge we facxe in a wide-area setting is maximixing epressiveness in the selection mechanism without sacrificing scalability in the delivery mechanism. "

"Intuitively, a simple event notification service that provides no selection mechnaism can be reduced to a multicast routing and transport mechanism for which there are numerous scalable implementations.  However, once the service provides a selection mechanism, then the overall efficiency of the service and its routing of notifications are affected by the power of the language used to construct notifications and to express filters and patterns.  As the power of the language increases, so does the complexity of the processing.  Thus, in practice, scalability and expressiveness are two conflicting goals that must be traded off." 

"Siera is an event notification service that we have designed and implemented to maximize both expressiveness and scalabiltiy."- goto