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Extending Informix®Beyond standard relational database objects, HCL Informix® can be extended to handle specialized data types, access methods, routines, and other objects. Informix® includes many built-in extensions that are fully integrated in the database server. Informix® also provides DataBlade® modules, which are packages of extended database objects for a particular purpose and that are installed separately from the database server. Alternatively, you can create your own user-defined objects for Informix®.
Creating extensionsYou can create user-defined data types, routines, access methods, and other database objects to suit your needs. You can use application programming interfaces to write user-defined routines and applications that access data in Informix® databases.
Virtual-Index Interface GuideThe Informix® Virtual-Index Interface Programmer's Guide explains how to create a secondary access method with the Virtual-Index Interface (VII) to extend the built-in indexing schemes of HCL Informix® typically with a DataBlade® module.
Develop an access methodThese topics describe the steps that you take to implement a user-defined access method with the Virtual-Index Interface (VII).
Specify an operator class
Add a default operator class to the access methodEvery access method must have at least one operator class so that the query optimizer knows which strategy and support functions apply to the index.

Add a default operator class to the access method

Every access method must have at least one operator class so that the query optimizer knows which strategy and support functions apply to the index.

You assign a default operator class so that the database server can locate the strategy and support functions for an index if the CREATE INDEX statement does not specify them. To add an operator-class name as the default for the access method, set the am_defopclass purpose value in the sysams system catalog table. The following example shows how to set the am_defopclass purpose value:

ALTER ACCESS_METHOD my_virtual
   ADD AM_DEFOPCLASS = 'special_operators'

For more information, see The ALTER ACCESS_METHOD (+) statement. For more information about operator classes and strategy and support functions, see the Informix® User-Defined Routines and Data Types Developer's Guide.

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