We describe a method, which enables us to solve optimization
problems resulting from dual decomposition approaches. We make use of a
well-known cutting plane method of level-type. This method allows us, to get rid
of the compactness-condition for the resulting inner problems because the
described level method can handle infinite function values.
The principal aim of this paper is the description of an appropriate
oracle. The case of optimization problems with convex quadratic objective functions
and affine-linear constraints is fully exploited and a detailled algorithm
is given for the mentioned class of problems. Some numerical tests for
problems with exclusively finite function values close the paper. We compare
the standard method with a method using normalized subgradients.