Described are a client application-programming interface (API) in a service oriented architecture (SOA). A system includes an application client having application code, one or more service interfaces, and a processor. An enterprise service bus (ESB) having a service registry connects one or more service implementations with the application client through the ESB. A processor is configured to execute the application code to invoke at least one of the one or more service interfaces and request at least one of the one or more service implementations via a request message. The request message comprises application code language based objects requesting a service. The processor is further configured to dynamically create a service instance for the service message. The service instance comprises the service message formatted for transport in the ESB and an endpoint reference for the one of the one or more service implementations as determined by the service registry.