Extended Data Types in the Database
Extended data types are user-defined types, based on the primitive data types Boolean, integer, real, string, and date, and the composite type container. You can also base an extended data type on another extended data type. Extended data types can be used to define fields in tables as well as to define variables in code.
This feature is not implemented as a language construct. Extended data types are defined in the Application Object Tree (AOT) under the Data Dictionary\Extended Data Types node.