 after the trigger event has occurred, the outgoing transition corre- sponding to the action part of the rule (e.g., prs in the case of PDP1_rule1) is taken. In the general case, policy rules with the same trigger may have overlapping conditions, SO that more than one of them may be true at a given point in time. In that case, the choice between the possible actions is nondeterministic. For presentation purposes, the PESM diagram in Figure 5.7 describes success- ful execution only. Unsuccessful or exceptional executions (e.g., registration failure) maybe described using additional policy rules and possibly involving other collabo- ration uses. The actual (successful) execution of the tele-consultation service will follow one of the choices depicted by the PESM, and the choice is made dynamically each time. For each node of a PESM that is a composite subservice used in the service (e.g., the collaboration use pcrs of aided Registration in the teleconsul- tation PESM), a global PESM diagram is defined. For the tele-consultation ser- vice, there are two composite subcollaborations, the aided registration collaboration and the consultation collaboration. The PESM diagrams for these subcollaborations are given in Figures 5.8 and 5.9, respectively. Figure 5.8 shows the global PESM diagram for the aided registration service used in the tele-consultation service. For the convenience of the reader, each policy rule is shown as a note annotated to the appropriate branch of the PESM diagram. In the diagram, we use a simplified notation for the collaboration uses, where, for exam- ple, pcr (caller -> assisted caller, callee -> reg assister) call stands for the collaboration use pcr of the collaboration call, where the elementary roles caller and callee are bound to the composite roles assisted caller and reg assister, respectively. During aided Registration, the receptionist obtains the registration information from the patient during the call, and provides this information to the electronic tele-consultation service desk. A