1. A method of operation within a data processing system, the method comprising: before receiving a request to execute a statement that requires computation of a first function, associating the first function with a second function that returns a data type descriptor for the first function; receiving a request to execute the statement that requires computation of the first function to return data from a source; and in response to receiving the request to execute the statement, performing the steps of: executing the second function to obtain the data type descriptor that identifies one or more data types of result data that should be returned for the first function; registering the one or more data types with a data processing system; compiling the statement based on the registered one or more data types; executing the first function to obtain the result data; storing the result data obtained from the source in a format that reflects the registered one or more data types; and returning the result data as data in the format of the registered one or more data types; and wherein the method is performed by one or more computing devices.