CCS is an (augmented) contact free C/E system

A new class of Petri Nets, called Augmented Condition/Event Systems is defined, by slightly relaxing the condition for enabling events. One system, called ?CCS, from this class is used to give a new operational semantics to Milner's Calculus of Communicating Systems. The set of CCS agents together with the traditional, interleaving based, derivation relation is proved isomorphic to the case graph of ?CCS (when single transitions only are considered). Our achievement is twofold: first, we provide CCS with a semantics which is able to describe concurrency and causal dependencies between the actions the various agents can perform; second, we guarantee an adequate linguistic level for the particular class of Petri Nets which can be defined through CCS operators.