When you invoke a UDM on a UDT, Vantage searches the SYSUDTLIB database for a UDM that has the UDT as its first parameter followed by the same number of parameters as the method invocation.
If several UDMs have the same name, Vantage must determine which UDM to invoke. For more information, see Teradata Vantage™ - SQL External Routine Programming, B035-1147.