Stefano Antoniazzi Alessandro Balboni William Fornaciari X-Nets: A visual formalism for system specification and analysis. 71-78 1993 38 Microprocessing and Microprogramming 1-5 http://dx.doi.org/10.1016/0165-6074(93)90128-8 db/journals/jsa/jsa38.html#AntoniazziBF93