Tham khảo tài liệu 'petri net part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | An Inter-Working Petri Net Model between SIMPLE and IMPS for XDM Service 81 Petri net model for Subscribing Group Change as shown in Figure 2. The six places P18 P19 P20 P21 P22 P23 represent the state elements in internal channel in IWF. Fig. 2. The Petri net model of Subscribing Group Change This model describes the case of Subscribing Group State on the condition that the subscribing request is initiated from IMPS server. The case which indicates the subscribing request initiated from Shared XDMS is not in the same session with the case showed in Figure 2 and the groups which the two cases represent are different so the Petri net model which describes the case on the condition that the subscribing request is initiated from Shared XDMS should be set up in another model. In the construction process the corresponding places transitions and related arcs should be constructed in a reverse direction from the model described in Figure 2 according to real condition of the service implementation not simply constructed directly from the above model in the reverse direction. The two models are symmetrical in some degree. Because the model shown in Figure 2 has unexpected conflicts and deadlocks see the analysis of the model in the Section 4 it represents that the existing mapping may have 82 Petri Net Theory and Applications some exceptions or unconsidered issues. In order to make the conflicts and deadlocks free we construct the modified Petri net models as shown in Sub-Figure 4 b and Sub-Figure 4 e . Based on the model shown in Figure 2 we add a series of places and transitions to build the model shown in Sub-Figure 4 b and Sub-Figure 4 e for example add P9 in the external channel between Shared XDMS and IWF add T11 and T12 in the IWF. Some places and transitions added represent the new mappings such as T5 P9 and T12 represent a new mapping . the 487 Response of SIP sent from IWF to Shared XDMS while some represent the new state such as P39 represents the state in .
