  We develop a systematic framework for exclusive rare B decays of the type B
-> K(*)l+l- at large dilepton invariant mass q^2. It is based on an operator
product expansion (OPE) for the required matrix elements of the nonleptonic
weak Hamiltonian in this kinematic regime. Our treatment differs from previous
work by a simplified operator basis, the explicit calculation of matrix
elements of subleading operators, and by a quantitative estimate of duality
violation. The latter point is discussed in detail, including the connection
with the existence of an OPE and an illustration within a simple toy model.
