  We derive exactly scalar products and form factors for integrable higher-spin
XXZ chains through the algebraic Bethe-ansatz method. Here spin values are
arbitrary and different spins can be mixed. We show the affine quantum-group
symmetry, $U_q(\hat{sl_2})$, for the monodromy matrix of the XXZ spin chain,
and then obtain the exact expressions. Furthermore, through the quantum-group
symmetry we explicitly derive the diagonalized forms of the $B$ and $C$
operators in the $F$-basis for the spin-1/2 XXZ spin chain, which was
conjectured in the algebraic Bethe-ansatz calculation of the XXZ correlation
functions. The results should be fundamental in studying form factors and
correlation functions systematically for various solvable models associated
with the integrable XXZ spin chains.
