st registration, T: ? (Request registration, External, assisted caller) External, assisted caller) C: chatOnly, NeedsAssistance, C: videoOnly, NeedsAssistance, Reg assister.onDuty Reg assister.onDuty A: ! (RoleReq(chatB), A: ! (RoleReq(mcallee), PDP2_acc assisted caller,Reg assister), assisted caller,Reg assister), PlayRole (chatA) PlayRole (mcaller) G: ChattedTo(ChatA G: MCalledTo(MCallee) chatA vcaller mcaller Figure 5.23 Local PESM diagram for the assisted caller composite role used in the aided Registration collaboration with specializations of the call collaboration. How to Model Dynamic Service Composition Using UML 2.x 5.7.2 Changing the Initial Specification by Adding Authentication In this section, we explain how the methodology may be used to change an initial specification using the tele-consultation service as an example. Consider, for exam- ple, that after some period of use of the tele-consultation service, a security analysis recommends that authentication is required for direct registration to the electronic tele-consultation service desk. The analysis has determined that authentication is not required, for aided registration, as the patient speaks to the receptionist, and not directly to the electronic tele-consultation service desk. The specification of the service therefore needs to be adapted SO that authentication is carried out before registration. This is done by reiteration of Step 1, and the following steps. The collaboration diagram for the unilateral two-pass authentication (UTPA) is specified, and a collaboration use of UTPA is added to the tele-consultation collaboration as shown in Figure 5.24. During a reiteration of Step 2, the sequence diagram for UTPA shown in Figure 5.25 is specified. Teleconsultation DoctorT consultant consult administrator consultation authenticatorT TeleSvcDsk registrar pas : UTPA assisting consulter registrar authenticateeT registration pcrs:aided registeree Registration reg assister PatientT assisted caller receptionistT Figure 5.24 Collaboration overview d