  For a classical link, Milnor defined a family of isotopy invariants, called
Milnor $\overline{\mu}$-invariants. Recently, Chrisman extended Milnor
$\overline{\mu}$-invariants to welded links by a topological approach. The aim
of this paper is to show that Milnor $\overline{\mu}$-invariants can be
extended to welded links by a combinatorial approach. The proof contains an
alternative proof for the invariance of the original
$\overline{\mu}$-invariants of classical links.
