User-defined extended index types allow you to create and apply your own logic for the three primary components that make up how an index works. The three components are index maintenance, index search, and index exploitation. You define index maintenance and index search with the CREATE INDEX EXTENSION statement. Index exploitation occurs in the evaluation of the search method.
You can now create indexes on spatial objects stored in a database. Only a structured type or a distinct type column can use the index extension to create a user-defined extended index type on these objects.
See the Administration Guide: Implementation and the SQL Reference for more information.