Database developer-created custom functions, which are explicitly connected to UDTs are known as UDMs. All UDMs must reside on server.
UDMs can be used to create an interface to the UDT that is independent of the UDT's internal representation. This makes it possible to later 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 which use the UDT.