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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-Table Interface GuideThe Informix® Virtual-Table Interface Programmer's Guide explains how to create a primary access method with the Virtual-Table Interface (VTI) so that users have a single SQL interface to HCL Informix® tables and to data that does not conform to the storage scheme of HCL Informix®.
Develop an access methodThese topics describe the steps that you take to implement a user-defined access method with the Virtual-Table Interface (VTI).
Testing the access methodTo test the access method, take the same actions that users of the access method take to create and access virtual data.
Insert, query, and update data

Insert, query, and update data

If you want to test fragmented tables, use the SQL syntax in Fragmentation support. If you want to support user-configured options, use the SQL syntax in Provide configuration keywords.

You can provide support in the access method for CREATE TABLE statement keywords that affect transaction processing. For example, if a CREATE TABLE statement specifies the WITH ROWIDS keyword, the access method must add a column of visible row identifiers to the table and allow queries on row identifiers. If a CREATE TABLE statement specifies the LOCK MODE clause, the access method must impose and manage locks during data retrieval and update. To determine the state of a table during transaction processing, the access method calls VTI functions to determine the lock mode, data-entry constraints, referential constraints, and other state information.

A user sets the isolation level with commands such as SET ISOLATION and SET TRANSACTION or with configuration settings in the onconfig file. It is recommended that you document the isolation levels that the access method supports, as The mi_scan_isolevel() accessor function describes.

A database server administrator can use the onconfig file to set defaults for such things as isolation level, locking, logging, and sbspace name. For information about defaults that you can set for the test-environment onconfig file, see the Informix® Administrator's Guide.

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