In order to verify the correctness of semantic description and description capability about EMA by visual way

that are used for the mobility and collaboration in mobile collaboration computing

a novel model named Petri net description(PND)is proposed. PND is a Petri net description form. The Petri net expression for the basic calculus entity is given. Each act is expressed by transition

and all kinds of fore-and-aft environment variables of act are expressed by places. Then

all kinds of operation semantic relations of basic calculus entities are expressed by Petri net

and the weights of arcs are used to depict the interactional relations among acts and their fore-and-aft environments. The synthesized theory of Petri net is used in PND

and the model of dynamic complex environment is constructed by synthesizing simple Petri nets. The simulation results with color Petri net tool show that the PND has the right semantic

and provides a strong demonstration for EMA.