Database developer-created custom functions, which are explicitly connected to UDTs, are known as User-Defined-Methods (UDMs). All UDMs must reside on the database.
UDMs can be used to create an interface to the UDT that is independent of the internal representation of the UDT. This makes it possible to enhance a given UDT, even in cases where the internal representation of the UDT must be changed to support the enhancement, without changing all of the database applications that use the UDT.