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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.
Access methodsThis section describes access methods, explains why you create user-defined access methods, and shows you how to create user-defined access methods
Access-method componentsWhen you add an access method to HCL Informix®, you add, or register, a collection of C user-defined routines (UDRs) in the system catalog. These UDRs take advantage of the Informix® application programming interface (API), the Virtual-Index Interface (VII).
Components that the Informix® database server provides
Virtual-Index InterfaceThe Virtual-Index Interface (VII) consists of purpose functions, descriptors, and accessor functions.
Accessor functionsUnlike purpose functions, the Virtual-Index Interface (VII) supplies the full code for each accessor function. Accessor functions obtain and set specific information in descriptors.

Accessor functions

Unlike purpose functions, the Virtual-Index Interface (VII) supplies the full code for each accessor function. Accessor functions obtain and set specific information in descriptors.

For example, the access method can perform the following actions:

Call the mi_tab_name() accessor function to obtain the name of the index from the table descriptor.
Store state information, such as a file handle or LO handle, in shared memory and then call the mi_tab_setuserdata() to place the pointer to the handle in the table descriptor so that subsequent purpose functions can retrieve the handle.

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