  Euler's sum formula and its multi-variable and weighted generalizations form
a large class of the identities of multiple zeta values. In this paper we prove
a family of identities involving Bernoulli numbers and apply them to obtain
infinitely many weighted sum formulas for double zeta values and triple zeta
values where the weight coefficients are given by symmetric polynomials. We
give a general conjecture in arbitrary depth at the end of the paper.
