private function _getCriteriaNames( MW_Common_Criteria_Expression_Interface $expr )
	{
		if( $expr instanceof MW_Common_Criteria_Expression_Compare_Interface ) {
			return array( $expr->getName() );
		}

		if( $expr instanceof MW_Common_Criteria_Expression_Combine_Interface )
		{
			$list = array();
			foreach( $expr->getExpressions() as $item ) {
				$list = array_merge( $list, $this->_getCriteriaNames( $item ) );
			}
			return $list;
		}

		if( $expr instanceof MW_Common_Criteria_Expression_Sort_Interface ) {
			return array( $expr->getName() );
		}

		return array();
	}