public function GetVat()
    {
        $oVat = $this->GetFromInternalCache('ovat');
        if (is_null($oVat)) {
            $oVat = $this->GetFieldShopVat();
            if (is_null($oVat)) {
                $oShopConf = TdbShop::GetInstance();
                $oVat = $oShopConf->GetVat();
            }
            $this->SetInternalCache('ovat', $oVat);
        }

        return $oVat;
    }