@neauoire Not Petri nets, but related if you're into that kind of graph based computation approach... I was (still am) very fond of the Signal/Collect programming model (which also can drastically simplify the implementation and parallelization of various types of algorithms):
http://www.cs.cmu.edu/~wcohen/postscript/iswc-2010.pdf
http://www.semantic-web-journal.net/system/files/swj971.pdf
FWIW (as more concrete reference with more examples/diagrams) my own #LiterateProgramming #Clojure implementation & interpretation of some of these ideas is here: