Archiving process

Support & Bugs
1

I’m a newbie. I have some question about archiving process:

  1. Ex : VisitTime/VisitTime.php when archiving period :
function archivePeriod( $notification )
    {
        $archiveProcessing = $notification->getNotificationObject();
        $dataTableToSum = array( 
                'VisitTime_localTime',
                'VisitTime_serverTime',
        );
        $archiveProcessing->archiveDataTable($dataTableToSum);
    }

Because each table have different calculate so it have different notication ? what notification process 2 table above?

Can you write a article about the way piwik archiving database