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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.
Qualify dataTo qualify table rows, a secondary access method applies the functions and Boolean operators from the qualification descriptor to key columns. The access method actually retrieves the contents of the keys from an index rather than from the table. If the index keys qualify, the secondary access method returns identifiers that enable the database server to locate the whole row that includes those key values.
Support for query plan evaluationAt the start of a SELECT statement, the database server initiates query planning. A query plan specifies the steps that the database server takes to fulfill a query with optimal efficiency.

Support for query plan evaluation

At the start of a SELECT statement, the database server initiates query planning. A query plan specifies the steps that the database server takes to fulfill a query with optimal efficiency.

The database server includes an optimizer, which compares various combinations of operations and chooses the query plan from among alternative approaches. To help the optimizer select the best query plan, provide reliable information about the cost for using the access method to select data.

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