Petri nets (Wikipedia, online) were introduced by C. A. Petri in 1962 in his doctoral dissertation for the purposes of describing chemical processes. Since then, Petri nets have been widely studied and developed by researchers and engineers in manufacturing and automation areas (Abdallah and ElMaraghy, 1998; Chen and Li, 2011; Chen et al., 2011; Ezpeleta et al., 1995; Ghaari et al., 2003; Hu et al., 2010; Li et al., 2007; Piroddi et al., 2008). Petri nets can model concurrent systems and their behavior with a mathematical formalism.