  In the present paper, we prove an identity for the generating function of the
quadruple zeta values. Taking homogeneous parts on both sides of the identity
and substituting appropriate values for the variables, we obtain the sum
formula for quadruple zeta values. We also obtain its weighted analogues, which
include the formulas for this case proved by Guo and Xie (2009, J. Number
Theory 129, 2747--2765) and by Ong, Eie, and Liaw (2013, Int. J. Number Theory
9, 1185--1198).
