Descriptors
The application programming interface (API) that the HCL Informix® database
server provides with the Virtual-Index Interface (VII) consists primarily
of the following components:
- Opaque data structures, called descriptors, that the database server passes by reference to purpose functions
- Accessor functions that store and retrieve descriptor values
The Virtual-Index Interface (VII) provides the following
descriptors and accessor functions.
| Descriptor | Describes | Accessor- function prefix | See |
|---|---|---|---|
| key descriptor (MI_AM_KEY_DESC) | Index keys, strategy functions, and support functions | mi_key_ | Key descriptor |
| qualification descriptor (MI_AM_QUAL_DESC) | WHERE clause criteria | mi_qual_ | Qualification descriptor |
| row descriptor (MI_ROW) | Order and data types of projected columns | Various DataBlade® API functions | Informix DataBlade API Programmer's Guide |
| row-id descriptor (MI_AM_ROWID_DESC) | Indexed table row location | mi_id_ | Row-ID descriptor |
| scan descriptor (MI_AM_SCAN_DESC) | SELECT clause projection | mi_scan_ | Scan descriptor |
| statistics descriptor (MI_AM_ISTATS_DESC) | Distribution of values | mi_istats_ | Statistics descriptor |
| table descriptor (MI_AM_TABLE_DESC) | Index location and attributes | mi_tab_ | Table descriptor |
Each of the following sections describes the contents
of a descriptor and the name of the accessor function that retrieves
each descriptor field.
Important: Because the internal
structure of any VII descriptor might change, HCL Informix declares
them as opaque structures. To make a portable access method, always
use the access functions to extract or set descriptor values. Do not
access descriptor fields directly.