Manuel Silva. 50 years after the PhD thesis of Carl Adam Petri: A perspective. In Antonio Ramírez-Treviño, Ernesto López-Mellado, Jean-Jacques Lesage, Manuel Silva, editors, 11th International Workshop on Discrete Event Systems, WODES 2012, Guadalajara, Mexico, October 3-5, 2012. pages 13-20, International Federation of Automatic Control, 2012. [doi]