  The issue of holographic principle in the PP-wave limit of the AdS/CFT
correspondence is discussed, in the hope of clarifying some confusions in the
literature. We show that, in the plane-wave limit, the relation between the
partition function in the bulk and the gauge-invariant correlation functions on
the boundary should be interpreted on the basis of a tunneling picture in the
semi-classical approximation which is appropriate for the plane-wave limit.
This leads to a natural relation between Euclidean S-matrix in the bulk and the
short-distance operator-product expansion of the so-called BMN operators on the
boundary.
