docs: def addService(self, moduleName, serviceName, service):
          """
          Add a service instance to the application service pool.
  
          :param moduleName: <str> module name in which the service is located
          :param serviceName: <str> service name
          :param service: <object> service instance
          :return: <void>
          """
          serviceIdentifier = "{}.{}".format(moduleName, serviceName)
          if serviceIdentifier not in self._services:
              self._services[serviceIdentifier] = service
          else:
              message = "Application - addService() - " \
                        "A service with the identifier {} already exists." \
                        .format(serviceIdentifier)
              raise Exception(message)