(1) A function that duplicates the semantics of another function, called a source function. Only scalar and aggregate functions can be sourced functions. See also function, routine.
(2) A function that is implemented by another built-in or user-defined function that is already known to the database manager. This function can be a scalar function or an aggregate function; it returns a single value from a set of values (for example, MAX or AVG). See also external function, SQL function, built-in function.