基于参考节点嵌入的图可达性查询

针对k步可达性查询算法无法解决带距离约束的图可达性查询问题，提出基于参考节点嵌入的图可达性查询算法。首先，从所有节点中选出极少数有代表性的全局参考节点，预先计算所有节点与全局参考节点之间的最短路径距离；然后，采用最短路径树和范围最小值查询技术求得局部参考节点；接着，利用三角不等式关系得到查询点对距离范围；最后，根据查询条件中的距离值与查询点对距离范围上、下限值的大小关系，可快速得出可达性结论。针对社会关系网络和公路网络数据，将所提算法与Dijkstra算法、K-Reach算法进行实验对比测试。相较于K-Reach算法，其索引建立时间小4个数量级，其索引规模小2个数量级；相较于Dijkstra算法，在公路网络和社会关系网络中，直接得出可达性结论的比例分别为92%和78.6%，其查询时间大大缩短，分别降低了95.5%和92%。实验结果表明：所提算法能够通过使用较小的索引开销，实现在线查询计算复杂度的降低，可很好地解决既适用于有权图又适用于无权图带距离约束的可达性查询问题。

Graph reachability query based on reference node embedding

Focusing on the issue that the problem of graph reachability query with distance constraint can not be solved by k-step reachability algorithm, a method of graph reachability query based on reference node embedding was proposed. Firstly, a very small part of representative global reference nodes were selected from all nodes, the shortest path distance between all nodes and these global reference nodes were previously calculated. Then the local reference nodes were obtained through the technology of the shortest path tree and range minimum query. Next, distance range was obtained based on the triangle inequality relation. Lastly, according to the relationship between the distance in query condition and the distance range, a conclusion of reachability could be drawn quickly. Comparative tests were done on data of social network and road network, the proposed algorithm was compared with Dijkstra algorithm and K-Reach algorithm. Compared with K-Reach algorithm, the indexing time of the proposed algorithm was four orders of magnitude shorter, and the index size was two orders of magnitude smaller. Compared with Dijkstra algorithm, the proportion of drawing a reachability conclusion directly by the proposed algorithm was 92% in the New York Road network, while 78.6% in the Digital Bibliography & Library Project (DBLP) network, moreover, the running time was shortened greatly, which was reduced by 95.5% and 92% respectively. The experimental results demonstrate that the computational complexity of online queries is reduced with a small index cost through the method proposed in this paper, which is a good solution to graph reachability query with distance constraint, and suitable for weighted graph as well as unweighted graph.