Functions and operators (jointly referred to in this chapter as “functions”) can be used in many contexts. For example, you can use the operator “+” to add numbers, concatenate strings, or to add two user-defined data type values. The use of a function within a given context is called a function instance.

The definition of a function instance links a function definition and the function's arguments to a procedure (user-written executable procedure, not a database procedure) and a result (type and length). For every new function that you define, you must provide the DBMS Server with function instance definitions for its use. You must also provide the function instance definitions that define the use of your new data type with the functions with which you intend to use it.