DAG reduction: Fast Answering reachability queries
- Publication Type:
- Conference Proceeding
- Proceedings of the ACM SIGMOD International Conference on Management of Data, 2017, Part F127746 pp. 375 - 390
- Issue Date:
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© 2017 ACM. Answering reachability queries is one of the fundamental graph operations. The existing approaches build indexes and answer reachability queries on a directed acyclic graph (DAG) G, which is constructed by coalescing each strongly connected component of the given directed graph G into a node of G. Considering that G can still be large to be processed efficiently, there are studies to further reduceGto a smaller graph. However, these approaches suffer from either inefficiency in answering reachability queries, or cannot scale to large graphs. In this paper, we study DAG reduction to accelerate reachability query processing, which reduces the size of G by computing transitive reduction (TR) followed by computing equivalence reduction (ER). For TR, we propose a bottom-up algorithm, namely buTR, which removes from G all redundant edges to get the unique smallest DAG Gt satisfying that Gt has the same transitive closure as that of G. For ER, we propose a divide-and-conquer algorithm, namely linear-ER. Given the result Gt of TR, linear-ER gets a smaller DAG Gϵ in linear time based on equivalence relationship between nodes in G. Our DAG reduction approaches (TR and ER) significantly improve the cost of time and space, and can be scaled to large graphs. We confirm the efficiency of our approaches by extensive experimental studies for TR, ER, and reachability query processing using 20 real datasets.
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