public function execute($sql)
	{

		//put this in try...catch block for better error handling
		try{

			//check if there is a valid service instance
			if (! $this->validService() ) 
			{
				//throw exceptions
				throw new MySQLException("Not connected to a valid database service");

			}

			//execute query and return response object
			return $this->service->query($sql);

		}

		//diplay error message
		catch(MySQLException $MySQLExceptionObject){

			//display error message
			$MySQLExceptionObject->errorShow();

		}

	}