BORA: Routing and Aggregation for Distributed Processing of Spatio-Temporal Range Queries

This work tackles the problem of answer-aggregation for continuous spatio-temporal range queries in distributed settings. We assume a grid-like coverage of the spatial universe of discourse, in which each cell is governed by a Base Station (BS) that communicates with the mobile users in its zone, and is also equipped with a server that has Moving Objects Database (MOD) capabilities. The MOD server stores the data for the moving objects in a given cell, processes the continuous queries pertaining to that cell, and is connected to the MOD servers in the neighboring cells. We demonstrate that, when a range query that spans over more than one cell needs to have its answer computed for a user located in a particular cell, by intelligently combining the transmission and the aggregation of the partial results, substantial improvements can be achieved at the global level. Towards this end, we present the BORA (Bresenham-based Overlay for Routing and Aggregation) tree, which is used to combine the transmission and local data aggregation along the routes to the destination of the query's answer.