Skyline Cohesive Group Queries in Large Road-social Networks

Given a network with social and spatial information, cohesive group queries aim at finding a group of users, which are strongly connected and closely co-located. Most existing studies limit to finding groups either with the strongest social ties under certain spatial constraint or minimum spatial distance under certain social constraints. It is difficult for users to decide which constraints they need to choose and how to decide the priority of the constraints to meet their real requirements since the social constraint and spatial constraint are different in nature. In this paper, we take a new approach to consider the constraints equally and study a skyline query. Specifically, given a road-social network consisting of a road network Gr and a location-based social network Gs, we aim to find a set of skyline cohesive groups, in which each group cannot be dominated by any other group in terms of social cohesiveness and spatial cohesiveness. We find a group of users using social cohesiveness based on (k, c)-core (a k-core of size c) and spatial cohesiveness based on travel cost to a meeting point from group members. Such skyline problem is NP-hard as we need to explore the combinations of c vertices to check whether it is a qualified (k, c)-core. In this paper, we first provide exact solutions by developing efficient pruning strategies to filter out a large number of combinations which cannot form a (k, c)-core, and then propose highly efficient greedy solutions based on a newly designed cd-tree to keep the distance on the road network and social structural information simultaneously. Experimental results show that our exact methods run faster than the brute-force methods by 2-4 orders of magnitude in general, and our cd-tree based greedy methods can significantly reduce the computation cost by 1-4 order of magnitude while the extra travel cost is less than 5% compared to the exact method on multiple real road-social networks.