UML vs. Petri-Net 

 
"Effective modeling of complex concurrent systems requires a formalism that can capture essential properties such as nondeterminism, synchronization and parallelism. Petri nets offer a clean formalism for concurrency, however lack thorough modularization techniques. Object orientation offers formalism for highly reusable and modular systems, but lacks general concurrency features. There have been a number of attempts to combine Petri nets with Object Oriented concepts to profit from the strengths of both approaches "

--John Anil Saldhana and Sol M. Shatz, Department of Electrical Engineering and Computer Science University of Illinois at Chicago[see reference [1]]

Solution:

Let user design the UML and validate  it by converting  it into the Petri-Net.