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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.
Design decisionsThese topics present the choices that you make to optimize the performance and flexibility of the access method that you can create with the virtual-index interface (VII).
Process queries that involve a virtual indexThis section describes various options for processing a SELECT statement, or query, that involves a virtual index.

Process queries that involve a virtual index

This section describes various options for processing a SELECT statement, or query, that involves a virtual index.

An SQL query requests that the database server fetch and assemble stored data into rows. A SELECT statement often includes a WHERE clause that specifies the values that a row must have to qualify for selection.

Query processing involves the following actions:

Interpreting the scan and qualification descriptors
Scanning the index to select index entries
Optionally returning rows that satisfy the query
Maintaining cost and distribution information for the optimizer

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