Reactive maintenance of continuous queries

This work addresses the problem of maintaining the consistency of the answers to continuous queries which are posed by the users of the Moving Objects Databases (MOD). Assuming that the motion of the object is represented by a trajectory, we focus on the effect that the modifications to the trajectory data can have on the queries answer-set. In case a mobile user enters a road section in which an accident has occurred, which was not anticipated in the “expected ” traffic behavior, not only his trajectory needs to updated, but the answer to the query that he posed may need to be recalculated and transmitted again. In this work we propose a framework which enables detecting and processing the pending queries whose answers need to be re-evaluated upon modifications to the MOD. We identify the relevant syntactic elements which can be extracted from the user’s queries and we analyze their semantic implications. We also propose an architecture of a system that can be used for this task. We demonstrate how triggers can be used to maintain the answers to the users ’ queries “up to date ” with respect to the modifications to the MOD and we show that our framework can be implemented on top of the existing ORDBMS. I