Updating and querying databases that track mobile units

In this paper, we consider databases representing information about moving objects (e.g., vehicles), particularly their location. We address the probl ems of updating and querying such databases. Specifically, the update probl em is to determine when the location of a moving object in the database (na mely its database location) should be updated. We answer this question by p roposing an information cost model that captures uncertainty, deviation, an d communication. Then we analyze dead-reckoning policies, namely policies t hat update the database location whenever the distance between the actual l ocation and the database location exceeds a given threshold, x. Dead-reckon ing is the prevalent approach in military applications, and our cost model enables us to determine the threshold x. We propose several dead-reckoning policies and we compare their performance by simulation. Then we consider the problem of processing range queries in the database. A n example of a range query is 'retrieve the objects that are currently insi de a given polygon P'. We propose a probabilistic approach to solve the pro blem. Namely, the DBMS will answer such a query with a set of objects, each of which is associated with a probability that the object is inside P.