The aim of this paper is to showhowany process of a Petri net which is a composition of two nets can be decomposed in processes of the component nets, and vice versa. Therefore, we introduce the concept of a process sample of a net with respect to a subnet and we claim that, under some requirements, jumping nets are suitable to generate all the process samples of a net. Then we give sufficient conditions under which a jumping Petri net can be simulated by a Petri net. Finally, a methodology for validation of Petri net models based on process decomposition, is proposed