On correlation functions of integrable models associated to the   six-vertex R-matrix
  We derive an analog of the master equation obtained recently for correlation functions of the XXZ chain for a wide class of quantum integrable systems described by the R-matrix of the six-vertex model, including in particular continuum models. This generalized master equation allows us to obtain multiple integral representations for the correlation functions of these models. We apply this method to derive the density-density correlation functions of the quantum non-linear Schrodinger model. 
N. Kitanine, K. Kozlowski, J. M. Maillet, N. A. Slavnov, V. Terras