As mobile devices with positioning capabilities continue to proliferate, data
management for so-called trajectory databases that capture the historical
movements of populations of moving objects becomes important. This paper
considers the querying of such databases for convoys, a convoy being a group of
objects that have traveled together for some time. More specifically, this
paper formalizes the concept of a convoy query using density-based notions, in
order to capture groups of arbitrary extents and shapes.