To model hardware and embedded applications, a highly concurrent model of computation is required. The PN domain in Ptolemy II presents a mechanism to model concurrency using the Kahn process networks model of computation . The process networks model of computation has a dataflow flavor to it. This makes it well suited to modeling embedded dataflow applications and hardware architectures.
In Ptolemy II, an implementation of the Kahn-MacQueen  semantics is provided. This is the bounded memory execution as proposed by T. Parks .
The following are the most important features of the operational semantics of PN as proposed by Kahn and MacQueen:
The above features make the execution of the network deterministic. The implementation in Ptolemy II is based on Java threads and synchronizing monitors.
In addition to the above features, the PN domain has been extended to support a notion of global time. Time advances for a PN process either when the process is blocked on a read from some channel or when is explicitly waiting for time to advance. This is based primarily on Pamela .
PN has been further extended to support dynamic changes to a graph. In case of timed-PN these changes are completely deterministic, while in case of untimed-PN, the changes could be non-deterministic and can depend on the schedule of the underlying java threads.