Without partner and partnerlink, the service is statically bound to a service implementation process located in the same project. In the case when the service is provided by a third party, or if there are multiple third parties providing the same service, you can use partner link to link the service with the partners. If you find a new provider, just add it to the partner link. The service providers maintain their service. When they change, you do not need to change the service as long as they do not change the contract (i.e. abstract WSDL).  That is,  Invoke partner uses an bstract WSDL to communicate with partner while SOAP R/R uses concrete WSDL. See the BW document "Palette Reference" on the topic "Partner and PartnerLink". There is an example project "invoke_partner"  in the tibco/bw/5.x/service/Invoke_partner directory.