Efficient algorithms for reachability and path queries on temporal bipartite graphs

Bipartite graphs are naturally used to model relationships between two types of entities, such as people-location, user-post, and investor-stock. When modeling real-world applications like disease outbreaks, edges are often enriched with temporal information, leading to temporal bipartite graphs. While reachability has been extensively studied on (temporal) unipartite graphs, it remains largely unexplored on temporal bipartite graphs. To fill this research gap, we study the reachability problem on temporal bipartite graphs in this paper. Specifically, a vertex u reaches a vertex w in a temporal bipartite graph G if u and w are connected through a series of consecutive wedges with time constraints. To efficiently answer if a vertex can reach the other vertex, we propose an index-based method by adapting the idea of 2-hop labeling. Effective optimization strategies and parallelization techniques are devised to accelerate the index construction process. To better support real-life scenarios, we further show how the index is leveraged to efficiently answer other types of queries, e.g., single-source reachability and earliest-arrival path queries. In addition, we propose an efficient method to handle incremental maintenance of the index structure. Extensive experiments on 16 real-world graphs demonstrate the effectiveness and efficiency of our proposed techniques.