Generators of von Neumann algebras associated with spectral measures

Let PE be the set of all values of a spectral measure E and A(PE) be the smallest von Neumann algebra containing PE. We give a simple description of all sets of generators of A(PE) in terms of the integrals with respect to E. The treatment covers not only the case of generators belonging to A(PE), but also the case of (possibly unbounded) generators affiliated with this algebra.