UML, being the industry standard as a common OO modeling language, needs a welldefined semantic base for its notation. Formalization of the graphical notation enables automated processing and analysis tasks. This paper describes a methodology for synthesis of a Petri net model from UML diagrams. The approach is based on deriving Object Net Models from UML statechart diagrams and connecting these object models based on UML collaboration diagram information. The resulting system-level Petri net model can be used as a foundation for formal Petri net analysis and simulation techniques. The methodology is illustrated on some small examples and a larger case study. The case study reveals some unexpected invalid system-state situations. Int. J. Soft. Eng. Knowl. Eng. 2001.11:643-673. Downloaded from www.worldscientific.com by CHINESE UNIVERSITY OF HONG KONG on 02/05/15. For personal use only. 644 J. A. Saldhana, S. M. Shatz & Z. Huization of ordinary PNs, allowing convenient definition and manipulation of data values. CPNs also have a formal, mathematical representation with a well-defined syntax and semantics.We suggest that design knowledge can be captured and formalized by the methodology outlined in Fig. 1. The methodology can enable a UML designer to verify UML models. In this paper, we focus on the key step of deriving an Object Petri net (OPN) from UML diagrams. We start with UML models as created by a system designer (appropriate UML editors can be used to develop UML statechart and collaboration diagrams). In our methodology, statechart diagrams are first converted to flat state machines. These state machines are then converted to a form of OPN called Object Net Models (discussed in Sec. 3). Then the UML collaboration diagrams are used to connect these object models to derive a single CPN for the system under study. Any standard CPN analyzer can be used to support analysis and simulation of the resulting CPN. This framework has the advantage of exploiting the mature theory and tools for Petri nets and essentially hiding these details from the end-user.