a user-defined data type that can be used in the same way as a built-in data type
a user-defined data type that is fully encapsulated, that is, whose internal structure is unknown to the database server
A fundamental data type of a predefined fixed or variable length whose internal structure is not accessible through SQL statements. Opaque data types are created with the SQL statement CREATE OPAQUE TYPE. Support functions must always be defined for opaque types.
An extended data type that contains one or more members but whose internal structure is interpreted by the database server using user-defined support routines.
