Hello Lin,

I was looking around on the net for information about methods of
specification, and I found some nice stuff on Petri-Nets...

First, a Petri-Net simulator... for Unix and in Java - free
http://www.ee.uwa.edu.au/~braunl/pns/

Petri-Net World - the Petri-Net Homepage
http://www.informatik.uni-hamburg.de/TGI/PetriNets/

Enjoy
-Nick

--
Nicholas Floersch