public function newFieldDefinitionCreateStruct($identifier, $fieldTypeIdentifier)
    {
        if (!is_string($identifier)) {
            throw new InvalidArgumentValue('$identifier', $identifier);
        }

        if (!is_string($fieldTypeIdentifier)) {
            throw new InvalidArgumentValue('$fieldTypeIdentifier', $fieldTypeIdentifier);
        }

        return new FieldDefinitionCreateStruct(
            array(
                'identifier' => $identifier,
                'fieldTypeIdentifier' => $fieldTypeIdentifier,
            )
        );
    }