Cohesive group nearest neighbor queries over road-social networks

The group nearest neighbor (GNN) search on a road network Gr, i.e., finding the spatial objects as activity assembly points with the smallest sum of distances to query users on Gr, has been extensively studied; however, previous works have neglected the fact that social relationships among query users, which ensure the maximally favorable atmosphere in the activity, can play an important role in GNN queries. Many real-world applications, such as location-based social networking services, require such queries. In this paper, we study a new problem: a GNN search on a road network that incorporates cohesive social relationships (CGNN). Specifically, both the query users of highest closeness and the corresponding top-j objects are retrieved. One critical challenge is to speed up the computation of CGNN queries over large social and road networks. To address this challenge, we propose a filtering-and-verification framework for efficient query processing. During filtering, we prune substantial unpromising users and objects using social and geographically spatial constraints. During verification, we obtain the object candidates, among which the top j are selected, with respect to the qualified users. Moreover, we further optimize search strategies to improve query performance. Finally, experimental results on real social and road networks significantly demonstrate the efficiency and efficacy of our solutions.