es) that are not changed under dynamic composition. Figure 5.3 shows an elementary collaboration for the registration How to Model Dynamic Service Composition Using UML 2.x Tele-consultation Consultant DoctorT consultation Consult administrator Consulter TeleSvcDsk registration Registrar Registeree Assisting Assisted registrar caller pcrs: aided Patient registration Reg assister Receptionist T Figure 5.2 Collaboration overview diagram for the basic tele-consultation service. service. The registration collaboration models the registration of a patient's request for consultation with a doctor. The two elementary roles (registeree and reg- - istrar) are bound to the PatientT and TeleSvcDsk composite roles, respec- tively. The visible interface behavior associated with an elementary collaboration may be modeled using, for example, UML 2.x interactions or semantic interfaces [2]. For ensuring correct dynamic composition in the runtime system, the visible interface behavior between the two elementary roles should be validated with respect to safety and liveness properties [11,12]. Composite roles are dynamic compositions of elementary roles and may also be compositions of composite roles. PatientT is a composite role playing the registeree elementary role, and the consulter and assisted caller Registration Registeree Registrar Figure 5.3 Elementary collaboration for a registration service. Service Delivery Platforms composite roles. Composite roles play elementary roles and/or composite roles governed by local composition policies as described later in Section 5.5. In Figure 5.2, there are three subcollaborations used in the composed service. The registration collaboration is an elementary collaboration for which the two elementary roles (registeree and registrar) are bound to the PatientT and TeleSvcDsk composite roles, respectively. There are two com- posite subcollaborations that are used in the teleconsultation collaboration. One of these, shown in Figure 5.4, is the aided Registration collaboration for which the c