A PARTIAL ORDER SEMANTICS FOR FIFO-NETS

In this work, we give a true concurrency semantics for FIFO-nets, that are Petri nets in which places behave as queues, tokens take values i n a finite alphabet and the firing of a transition depends on sequence s on the alphabet. We introduce fn-processes to represent the concurre nt behavior of a FIFO-net N during a sequence of transition firings. F n-processes are modeled by a mapping from a simple FIFO-net without qu eue sharing and cycles, named FIFO-occurrence net, to N. Moreover, the relation among the firings expressed by the FIFO-occurrence net has b een enriched by an ordering relation among the elements of the FIFO-oc currence net representing values entered into a same queue of N. We gi ve a way to build fn-processes step by step in correspondance with a s equence of transition firings and the fn-processes operationally built are all those abstractly defined. The FIFO-occurrence nets of fn-proc esses have some interesting properties; for example, such nets are alw ays discrete and, consequently, there is at least a transition sequenc e corresponding to each fn-process.