Laura Recalde Enrique Teruel Manuel Silva {SC}*ECS: A Class of Modular and Hierarchical Cooperating Systems. 440-459 1996 conf/apn/1996 Application and Theory of Petri Nets db/conf/apn/apn96.html#RecaldeTS96 http://dx.doi.org/10.1007/3-540-61363-3_24