A Data Stream Publish/Subscribe Architecture with Self-adapting Queries

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 use the formalism to develop methods to adapt query plans to changes in the set of available data streams and allow consumers to dynamically change which streams they subscribe to.