public function isItemModelDefined(core_kernel_classes_Resource $item)
    {
        $returnValue = (bool)false;

        if (!is_null($item)) {

            $model = $item->getOnePropertyValue($this->itemModelProperty);
            if ($model instanceof core_kernel_classes_Literal) {
                if (strlen((string)$model) > 0) {
                    $returnValue = true;
                }
            } else if (!is_null($model)) {
                $returnValue = true;
            }
        }

        return (bool)$returnValue;
    }