  In PODS'21, Hu presented an algorithm in the massively parallel computation
(MPC) model that processes any acyclic join with an asymptotically optimal
load. In this paper, we present an alternative analysis of her algorithm. The
novelty of our analysis is in the revelation of a new mathematical structure --
which we name "canonical edge cover" -- for acyclic hypergraphs. We prove
non-trivial properties for canonical edge covers that offer us a
graph-theoretic perspective about why Hu's algorithm works.
