Generators of von Neumann algebras associated with spectral measures

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