Before revision:  In an experimental study, we compare a variety of algorithms with respect to their index-building and query times as well as their memory footprint . All of them yield a time/space trade-off for queries.
After revision:  In an experimental study, we compare a variety of algorithms with respect to their index-building and query times as well as their memory footprint on a diverse set of instances. Our experiments indicate that the query performance often depends strongly not only on the type of graph, but also on the result, i.e., reachable or unreachable. Furthermore, we show that previous algorithms are significantly sped up when combined with our new approach in almost all scenarios.