Time Period-Based Top-k Semantic Trajectory Pattern Query.

The sequences of user check-ins form semantic trajectories that represent the movement of users through time, along with the types of POIs visited. Extracting patterns in semantic trajectories can be widely used in applications such as route planning and trip recommendation. Existing studies focus on the entire time duration of the data, which may miss some temporally significant patterns. In addition, they require thresholds to define the interestingness of the patterns. Motivated by the above, we study a new problem of finding top-k semantic trajectory patterns w.r.t. a given time period and given categories by considering the spatial closeness of POIs. Specifically, we propose a novel algorithm, EC2M that converts the problem from POI-based to cluster-based pattern search and progressively consider pattern sequences with efficient pruning strategies at different steps. Two hashmap structures are proposed to validate the spatial closeness of the trajectories that constitute temporally relevant patterns. Experimental results on real-life trajectory data verify both the efficiency and effectiveness of our method.