  The paper "Stack-based Algorithms for Pattern Matching on DAGs" generalizes
the classical holistic twig join algorithms and proposes PathStackD, TwigStackD
and DagStackD to respectively evaluate path, twig and DAG pattern queries on
directed acyclic graphs. In this paper, we investigate the major results of
that paper, pointing out several discrepancies and proposing solutions to
resolving them. We show that the original algorithms do not find particular
types of query solutions that are common in practice. We also analyze the
effect of an underlying assumption on the correctness of the algorithms and
discuss the pre-filtering process that the original work proposes to prune
redundant nodes. Our experimental study on both real and synthetic data
substantiates our conclusions.
