protected function getDataPoolSkeleton()
    {
        // Default skeleton containing entries at the 1st level
        return [
            Doozr_Form_Service_Constant::IDENTIFIER_DATA          => [],                                                   // Valid! values after validation
            Doozr_Form_Service_Constant::IDENTIFIER_FILES         => [],                                                   // Valid! files after validation
            Doozr_Form_Service_Constant::IDENTIFIER_COMPONENTS    => [],                                                   // Form components of current step
            Doozr_Form_Service_Constant::IDENTIFIER_METHOD        => Doozr_Form_Service_Constant::METHOD_GET,              // Method to use for transport
            Doozr_Form_Service_Constant::IDENTIFIER_STEP          => Doozr_Form_Service_Constant::DEFAULT_STEP_FIRST,      // Active step
            Doozr_Form_Service_Constant::IDENTIFIER_STEPS         => Doozr_Form_Service_Constant::DEFAULT_STEP_LAST,       // Last step
            Doozr_Form_Service_Constant::IDENTIFIER_TOKEN         => null,                                                 // Token for next request/response
            Doozr_Form_Service_Constant::IDENTIFIER_TOKENBEHAVIOR => Doozr_Form_Service_Constant::DEFAULT_TOKEN_BEHAVIOR,  // How to behave on invalid token
            Doozr_Form_Service_Constant::IDENTIFIER_LASTVALIDSTEP => null,                                                 // Last successful validated step
            Doozr_Form_Service_Constant::IDENTIFIER_UPLOAD        => Doozr_Form_Service_Constant::DEFAULT_HAS_FILE_UPLOAD, // Whether the form has an upload
        ];
    }