The Wikipedia article on Direct Integrals gives the following remark on the definition (of the direct integral of Hilbert spaces):
This definition is apparently more restrictive than the one given by von Neumann and discussed in Dixmier's classic treatise on von Neumann algebras...One of the main theorems of the von Neumann theory is to show that in fact the more general definition can be reduced to the simpler one given here.
Does anyone know of a reference where the 'more restrictive definition' given in the Wikipedia article is proved to be equivalent to a more 'classical definition'?