entT.consulted PatientT.consulted pcd (consult administrator >TeleSvcDsk, consultant -> DoctorT, consulter -> PatientT): consultation Figure 5.7 Global PESM diagram for the tele-consultation service. composed. The PESM is modeled as a graph defining the flow of invocations of collaborations represented as nodes. As nodes, the PESM contains collaboration uses, each consisting of a collabora- tion use name (e.g., prs), a collaboration name (e.g., registration), and the roles as bound to composite roles (e.g., registeree bound to PatientT and registrar bound to TeleSvcDsk). The collaboration uses are linked by transitions and choice nodes. The initial state represents the start of execution of the composite services represented by the PESM. The nodes are collaboration uses linked by transitions (->) and choice nodes (<). The choice nodes are labeled as numbered policy decision points (PDPs) SO that the policy rules can be stored with a pointer to the PDP they apply to. Each PDP refers to a set of policy rules (one or more). For the convenience of the reader, each policy rule is shown as a note annotated to the appropriate branch of the PESM diagram. At each PDP, policy-ruled choice is evaluated, and the outgoing transition chosen is policy ruled. In Figure 5.7, the first policy decision point (PDP1) points to two global policy rules, governing a choice between execution of registration and aided Service Delivery Platforms registration. The choice is made in PDP1, when the PatientT composite role receives a request for registration. This request is the trigger event for both policy rules in PDP1, and which outgoing transition to be taken will then depend on the conditions in the policy rules. In this example, the condition C of PDP1_Rule1 states that the policy only applies when the instance playing the PatientT composite role is a Patient of the Doctor represented by the DoctorT composite role, PatientT does not require assistance, and that the TeleSvcDsk is on line. If the condition of a rule is evalu- ated as true