$HT$ : A Novel Labeling Scheme for k-Hop Reachability Queries on DAGs

Given a directed acyclic graph (
DAG
), a
$k$
-hop reachability query
${u}\xrightarrow {?k}{v}$
is used to answer whether there exists a path from
$u$
to
$v$
with length
$\leq k$
. Answering
$k$
-hop reachability queries is a fundamental graph operation and has been extensively studied during the past years. Considering that existing approaches still suffer from inefficiency in practice when processing large graphs, we propose a novel labeling scheme, namely
HT
, to accelerate
$k$
-hop reachability queries answering.
HT
uses a constrained 2hop distance label to maintain the length of shortest paths between a set of hop nodes and other nodes, and for the remaining reachability information,
HT
uses a novel topological level to accelerate graph traversal. Further, we propose to enhance
HT
by two optimization techniques. The experimental results show that compared with the state-of-the-art approaches,
HT
works best for most graphs when answering
$k$
-hop reachability queries with small index size and reasonable index construction time.