PETRI NETS AS EXECUTABLE SPECIFICATIONS OF HIGH-LEVEL TIMED PARALLEL SYSTEMS

Abstra t. We propose to use high-level Petri nets as a model for the semanti s of high-level parallel systems. This model is known to be useful for the purpose of veri ation and we show that it is also exe utable in a parallel way. Exe uting a Petri net is not di ult in general but more ompli ated in a timed ontext, whi h makes ne essary to syn hronise the internal time of the Petri net with the real time of its environment. Another problem is to relate the exe ution of a Petri net, whi h has its own semanti s, to that of its environment; i. e., to properly handle input/output. This paper presents a parallel algorithm to exe ute Petri nets with time, enfor ing the even progression of internal time with respe t to that of the real time and allowing the ex hange of information with the environment. We dene a lass of Petri nets suitable for a parallel exe ution ma hine whi h preserves the step sequen e semanti s of the nets and ensures time onsistent exe utions while taking into a ount the soli itation of its environment. The question of the e ient veri ation of su h nets has been addressed in a separate paper [14℄, the present one is more fo used on the pra ti al aspe ts involved in the exe ution of so modelled systems. Key words. Petri nets, parallelism, real-time, exe ution ma hines. 1. Introdu tion. Petri nets are widely used as a model of on urren y, whi h allows to represent the o urren e of independent events. They an be as well a model of parallelism, where the simultaneity of the events is more important. Indeed, when we onsider their step sequen e semanti s, an exe ution is represente