ctorT) administrator, consultant) consultant) C: AvailableForConsultation C: True, AvailableForConsultation, C: AvailableForConsultation A: PlayRole (consultant) consulter.registered A: PlayRole (adminUser) G: consultationComplete A: ! (RoleReq(callee), consultant, G: adminUseComplete consulter), PlayRole (caller) G: TalkedTo(Callee) PDP4_D PDP5_ct PDP6_ct Caller Consultant adminUser Figure 5.14 Local PESM diagram for the DoctorT composite role. In the next sections, we present the general methodology for model-driven policy-enabled dynamic composition of services. The practical usage of the meth- odology is explained through its use in the tele-consultation service. 5.6 Methodology The methodology follows the three-layered approach from Section 5.2. localPESM Receptionist T localPESM reg assister PDP3_ra_Rule1 PDP2_ra_Rule1 T: ! (Answer, Reg assister, PDP1_R_Rule2: T: ? (RoleReq(callee), assisted caller) T: ? (RoleReq(reg assister), assisted caller, Reg assister) C: True, AssistedcallerInCall, Patient T, ReceptionistT) C: onDuty assisting register.onLine C: onDuty A: PlayRole (callee) A: ! (RoleReq(registrar), Reg assister, A: PlayRole (reg assister) G: TalkedTo(Caller) assisting registrar), G: assistedRegistrationComplete PlayRole (registeree) G: AssistedcallerRegistered, PDP1_R PDP2_ra PDP3_ra Reg assister Callee Registeree Figure 5.15 Local PESM diagram for the ReceptionistT composite role. How to Model Dynamic Service Composition Using UML 2.x 5.6.1 The Service Model Layer In this section, we address the steps involved at the service model layer. Step 1: Specify the service (or family of services) Use a UML 2.x collaboration overview diagram to describe 1. The distributed parts involved in the composed service, given as one compos- ite role for each part. 2. The set of collaboration uses involved in the composed service. Each collabo- ration use is specified in one of the following ways: a. Either, as an elementary collaboration, that is, a collaboration between exactly two elementary roles, b. Or, as a comp