Polymorphism is a foundational concept within the object-oriented paradigm and is a feature of any mainstream object-oriented language that supports reusability and abstraction in software designs. With fUML being a standard specification of execution semantics of UML activity diagrams, it defines functionalities to simulate polymorphic behavior within such model executions. fUML only provides a simple standard implementation for simulating dynamic polymorphism at runtime. This default implementation does not meet the criteria of polymorphism as it is well-known and established by most mainstream object-oriented programming languages over the last decades, nor does it comply with the constraints for method overriding imposed by the original UML specification. However, fUML offers extension capabilities to add user-defined behavior for semantic variation points like polymorphism handling. This paper presents an extension of fUML execution semantics, enabling refined and more sophisticated simulation of polymorphism for executable UML models to comply with UML and the general understanding and functioning principles of polymorphic behavior within the object-oriented paradigm.

OMG's PSCS specification extends the execution model of fUML by precise runtime semantics for UML composite structures. With composite structures being a concept for describing structural properties of a model, the majority of execution semantics specified by PSCS concern analysis and processing of static information about the model's fine-grained structure at runtime. Using Model-To-Text-Transformation to generate source code, which serves as an input for PSCS's actual execution environment, the runtime level of model execution can be relieved by outsourcing analysis and processing of static information to the level of code generation. By inserting this step of preprocessing, the performance of the actual model execution at runtime can be improved. This paper introduces an implementation of the PSCS specification for C++ based on code generation using Model-to-Text-Transformation. Moreover, it presents a set of test models validating the correct functionality of the implementation a s well as a performance benchmark. The PSCS implementation presented by this paper was developed as a part of the MDE4CPP* project.