private function _registerService($className, $constructorType) {
        if (!class_exists($className)) {
            $errorMsg = sprintf(self::ERROR_CLASS_NOT_FOUND, $className);
            throw new ulfberhtException($errorMsg);
        } elseif ($this->has($className)) {
            $errorMsg = sprintf(self::ERROR_CLASS_ALREADY_DEFINED, $className);
            throw new ulfberhtException($errorMsg);
        }

        $this->_services[$className] = new serviceWrapper(
            $className,
            $constructorType
        );
        $this->_serviceDependencyGraph->addResource($className);
        $this->_serviceDependencyGraph->addDependencies(
            $className,
            $this->_services[$className]->dependencies
        );
    }