Republishers in a Publish/Subscribe Architecture for Data Streams

In data stream applications, streams typically arise from a geographically distributed collection of producers and may be queried by consumers, which may be distributed as well. In such a setting, a query can be seen as a subscription asking to be informed of all tuples that satisfy a specific condition. We propose to support the publishing and querying of distributed data streams by a publish/subscribe architecture. To enable such a system to scale to a large number of producers and consumers requires the introduction of republishers which collect together data streams and make the merged stream available. If republishers consume from other republishers, a hierarchy of republishers results. We present a formalism that allows distributed data streams, published by independent stream producers, to be integrated as views on a mediated schema. We then use this formalism to develop query planning techniques for the republishers, and methods to adapt plans when the set of available data streams changes.