Oracle provides extensible indexing to accommodate indexes on customized complex
datatypes such as documents, spatial data, images, and video clips and to make use of
specialized indexing techniques. With extensible indexing, you can encapsulate
application-specific index management routines as an indextype schema object and
define a domain index (an application-specific index) on table columns or attributes of
an object type. Extensible indexing also provides efficient processing of
application-specific operators.

The application software, called the cartridge, controls the structure and content of a
domain index. The Oracle database server interacts with the application to build,
maintain, and search the domain index. The index structure itself can be stored in the
Oracle database as an index-organized table or externally as a file.

应用域索引
1. 依据用户复杂的数据类型(文档，空间文件等）而支持的可扩展的索引
2. 域索引既能够以索引表的形式存储在 Oracle 数据库中，也能够以文件的形式存储在数据库外。