  We consider an algebraic structure of the $XXZ$ model in the gapless regime.
We argue that a certain degeneration limit of the elliptic algebra
$A_{q,p}(\widehat{sl_2})$ is a relevant object. We give a free boson
realization of this limiting algebra and derive an integral formula for the
correlation function. The result agrees with the one obtained by solving a
system of difference equations. We also discuss the relation of our algebra to
the deformed Virasoro algebra and Lukyanov's bosonization of the sine-Gordon
theory.
