The object extensions of DB2 enable you to realize many of the benefits of object technology while building on the strengths of relational technology. In a relational system, data types are used to describe the data stored in columns of tables where the instances (or objects) of these data types are stored. Operations on these instances are supported by means of operators or functions that can be invoked anywhere that expressions are allowed.
The DB2 approach to support object extensions fits exactly into the relational paradigm. UDTs are data types defined by the user which, like built-in types, can be used to describe the data stored in columns of tables. UDFs are functions defined by a user which, like built-in functions or operators, support the manipulation of UDT instances. Thus, UDT instances are stored in columns of tables and manipulated by UDFs in SQL queries. UDTs can be internally represented in different ways. LOBs are just one example of this.