Efficient reachability test on directed graphs and its application to large XML data

We propose an efficient algorithm for deciding the reachability between any nodes on XML data represented by connected directed graphs. In case of tree structures, the reachability is testable in a constant time by preprocessing the range labels of all nodes. However, in case of general directed graphs, it is impossible to set a simple range label for the graph even if it is acyclic. In this study, we introduce a new index for the problem of the reachability test on the general graphs. We show that our algorithm can check the reachability in almost constant time preserving the space efficiency and a reasonable preprocessing time compared with other methods.