James Cheng, Zechao Shang, Hong Cheng, Haixun Wang, and Jeffrey Yu
We study the problem of answering k-hop reachability queries in a directed graph, i.e., whether there exists a directed path of length k, from a source query vertex to a target query vertex in the in- put graph. The problem of k-hop reachability is a general problem of the classic reachability (where k = ∞). Existing indexes for processing classic reachability queries, as well as for processing shortest path queries, are not applicable or not efﬁcient for pro- cessing k-hop reachability queries. We propose an index for pro- cessing k-hop reachability queries, which is simple in design and efﬁcient to construct. Our experimental results on a wide range of real datasets show that our index is more efﬁcient than the state-of- the-art indexes even for processing classic reachability queries, for which these indexes are primarily designed. We also show that our index is efﬁcient in answering k-hop reachability queries.