Graphical mass factorization

We point to the close analogy between (multiplicative) BPHZ-renormalization and mass factorization. Adapation of the forest formula to mass singular graphs allows an alternative proof of mass factorization. A diagrammatic method is developed to carry out diagram-by-diagram mass factorization with the mass singularities being substracted by counter terms which built up the operator matrix element. The reasoning is exposed for deep-inelastic (DI) scattering and for the Drell-Yan (DY) process. (orig.)