Literature review suggests concentrating on the development of new reference model for manufacturing system simulation, which may implement an operation logic much closer to real industrial contexts. A production system modelling tool should be designed with the aim of standardizing and simplifying the simulation of manufacturing processes and to widespread this approach in {SMEs.} Pursuing this aim, the authors got committed in designing a reference model for providing a structural framework to support shop-floor simulation and optimization. This paper presents the basic framework logic and structure of the simulation tool, showing how it is possible to represent it in Business Process Modelling Notation {(BPMN).} The efforts of implementing an {MRP} module on top of a simulation tool, which was originally conceived to embed look-back material handling policies, are described together with the operative solutions chosen to reach the integration.