/**
  * Is this products stock quantity overbookable?
  * If this product does not have overbookablility set the general setting of
  * the config object is choosen.
  * If stock management is deactivated true will be returned.
  *
  * @return boolean is the product overbookable?
  *
  * @author Roland Lehmann <*****@*****.**>, Sebastian Diel <*****@*****.**>
  * @since 26.11.2012
  */
 public function isStockQuantityOverbookable()
 {
     if (is_null($this->isStockQuantityOverbookable)) {
         $overbookable = true;
         if (SilvercartConfig::EnableStockManagement()) {
             if (!SilvercartConfig::isStockManagementOverbookable() && !$this->StockQuantityOverbookable) {
                 $overbookable = false;
             }
         }
         $this->isStockQuantityOverbookable = $overbookable;
     }
     return $this->isStockQuantityOverbookable;
 }
 /**
  * May a products stock quantity be below zero?
  * 
  * @return bool is stock management overbookable?
  * 
  * @author Roland Lehmann <*****@*****.**>
  * @since 17.7.2011
  */
 public static function isStockManagementOverbookable()
 {
     if (is_null(self::$isStockManagementOverbookable)) {
         self::$isStockManagementOverbookable = self::getConfig()->isStockManagementOverbookable;
     }
     return self::$isStockManagementOverbookable;
 }