Span(Graph): A Categorial Algebra of Transition Systems. - Piergiulio Katis; Nicoletta Sabadini; Robert F. C. Walters (AMAST, 1997)

Representing Place/Transition Nets in Span(Graph). - Piergiulio Katis; Nicoletta Sabadini; Robert F. C. Walters (AMAST, 1997)

A Formalization of the IWIM Model. - Piergiulio Katis; Nicoletta Sabadini; Robert F. C. Walters (COORDINATION, 2000)

On Automata with Boundary - R. Gates; Piergiulio Katis; Nicoletta Sabadini; Robert F. C. Walters (CoRR, 2000)

Comparing cospan-spans and tiles via a Hoare-style process calculus. - Fabio Gadducci; Piergiulio Katis; Ugo Montanari; Nicoletta Sabadini; Robert F. C. Walters (TOSCA, 2001)

Feedback, trace and fixed-point semantics. - Piergiulio Katis; Nicoletta Sabadini; Robert F. C. Walters (RAIRO Theor. Informatics Appl., 2002)

Compositional Minimization in Span(Graph): Some Examples. - Piergiulio Katis; Nicoletta Sabadini; Robert F. C. Walters (COMETA, 2003)