An elementary Petri net based model for distributed system design

In this paper we discuss an elementary net (EN) based model in which there are 3 levels named L₁, L₂, L₃ respectively. In the level L₁ on an EN the arcs, events and places can be interpreted in order to use it easily in system design. In L₂, it is also a graphic model, each node has their own implementation by EN. More precisely there are two kinds of function nodes and two interface nodes in it. The function nodes have `parallel´, `choice´, `send´, and `receive´ for the nodes of interface. Using L₂ a three processors cooperative computing system is introduced to demonstrate the advantages of L₂. Considering the design complexity, a very high level model L₃ which is a model more higher than L₂, is established, in which there are three useful macros called `synchronization´, `decision´ and `guarded´. Modelling a two processors system by L₃ makes the model to have more sense