Continuous query evaluation over distributed sensor networks

In this paper we address the problem of processing continuous multi-join queries, over distributed data streams. Our approach makes use of existing work in the field of publish/subscribe systems. We show how these principles can be ported to our envisioned architectural model by enriching the common query model with location dependent attributes. We allow users to subscribe to a set of sensor attributes, a service that requires processing multi-join correlation queries. The goal is to decrease the overall network traffic consumption by removing redundant subscriptions and eliminating unrequested events close to the publishing sensors. This is non-trivial, especially in the presence of multi-join queries without any central control mechanism. Our approach is based on the concept of filter-split-forward phases for efficient subscription filtering and placement inside the network. We report on a performance evaluation using a real-world dataset, showing the improvements over the state-of-the-art, as we reduce the overall data traffic by half.