The article intends to highlight the particularities of the derivational morphology mechanisms that will help in lexical resources extension. Some computing approaches for derivational morphology are given for several languages, inclusively for Romanian. This paper deals with some preprocessing particularities that are needed in the process of automatic generation. Then, generative mechanisms are presented in the form of derivational formal rules separately for pre¯xation and su±xation. The article ends with several approaches in automatic new generated words validation.