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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.
Descriptor function reference
Descriptors
Key descriptorThe key descriptor, or MI_AM_KEY_DESC structure, identifies the keys and operator class for an index.

Key descriptor

The key descriptor, or MI_AM_KEY_DESC structure, identifies the keys and operator class for an index.

The following functions extract information from the key descriptor.


Accessor function	Return value
mi_key_funcid()	The routine identifier of the UDR that determines the value of a specified key in a functional index
mi_key_nkeys()	The number of columns in an index key
mi_key_opclass(), mi_key_opclass_name()	The identifier or name of the operator class for a specified column of the index key
mi_key_opclass_strat()	The name of one strategy function Typically, an access method calls the mi_qual_funcid() function to obtain the routine identifier and does not use mi_key_opclass_strat().
mi_key_opclass_nsupt()	The number of support functions
mi_key_opclass_supt()	The name of one support function For an example of how to use the function names to execute the function, see Obtaining the routine identifier.

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