Semantrix: A Compressed Semantic Matrix

Nieves Brisaboa, Antonio Fariña, Gonzalo Navarro, and Tirso Rodeiro

We present a compact data structure to represent both the duration and length of homogeneous fragments of trajectories from moving objects in a way that, as a data warehouse, it allows us to efficiently answer cumulative queries. The division of trajectories into relevant fragments has been studied in the literature under the topic of Semantic Trajectories. In this paper, we designed a data structure to compactly represent them and the algorithms to answer the more relevant queries. We experimentally evaluate our proposal into the real context of an enterprise with mobile workers (truck drivers) where we aim at analyzing the time they spend in different activities. To test our proposal under higher stress conditions we generated a huge amount of synthetic realistic trajectories and evaluated our system with those data to have a good idea about its space needs and its efficiency when answering different types of queries.