Double Hierarchical Labeling Shortest Distance Querying in Time-dependent Road Networks

A shortest distance query is a fundamental operation of various real-time response applications in time-dependent road networks. Unfortunately, existing methods (e.g., G-treelike, 2-hop labeling-like) are prohibitively expensive in terms of space/time. To this end, we propose a novel Double Hierarchical Labeling (DHL) index, which consists of a Hierarchical Graph Partition (HGP) tree and a hierarchical border labeling list. For HGP-tree, we first use a hierarchical graph partitioning to split the entire road network into hierarchical subgraphs and then index these subgraphs by a balanced tree. To preserve all connectivity information between border vertices of subgraphs, a Time-based Distance Inverted File (TDIF) is constructed for each leaf node of the HGP-tree. For the hierarchical labeling list, we construct it only for border vertices and use it to speed up query processing. Moreover, a label propagation update is proposed to manage label updating when weights change. Finally, we propose a phase-aware search algorithm for different search situations between given query vertices to guarantee query efficiency. Extensive experiments are conducted to demonstrate the superiority of the proposed proposals on query processing and index maintenance.