Trajectory data warehouses: design issues and use cases

In this paper we discuss how data warehousing technology can be used to store aggregate information about trajectories and to per- form OLAP operations over them. To this end, we define a data cube with spatial and temporal dimensions, discretized according to a hierarchy of regular grids. Moreover, we analyse some measures of interest related to trajectories, such as the number of trajectories starting from a cell, the distance covered by the trajectories in a cell, the average and maximum speed and the average acceleration of the trajectories in the cell. We provide some algorithms to compute and load these measures in the base cells, starting from a stream of trajectory observations. Such stored values are used, along with suitable aggregate functions, to compute the roll-up operations. Finally, we envision some use cases that would benefit from such a framework, in particular in the domain of supervision systems to monitor road traffic (or movements of individuals) in a given geographical area.