The paper presents an extensible Petri Net Markup Language (xPNML), which is an extended version of PNML. The xPNML format overcomes limitations associated with PNML structure for simulation and analysis of stochastic Petri nets. In addition, the proposed format supports modular concepts for creating specific models (for example, a module for machine operation including working, failed and repair states). These modules can be used as templates and exchanged among different net models. The paper provides the ontology of xPNML model and overview of its JAVA based implementation for simulation and analysis of stochastic Petri nets.