function is_available() {
        if ($this->_is_available === null) {
            $this->_is_available = true;

            $el = $this->element();
            if ($el['ACTIVE'] == 'N')
                $this->_is_available = false;
            if ($this->quantity() == 0)
                $this->_is_available = false;
        }

        return $this->_is_available;
    }