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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 extensions
You 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 Guide
The 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 method
These topics describe the steps that you take to implement a user-defined access method with the Virtual-Table Interface (VTI).

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.
- Informix® extensions and DataBlade® modules
  These topics describe how to use built-in database extensions and separately installed DataBlade® modules.
- Creating extensions
  You 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.
  - DataBlade® API Programmer's Guide
    The Informix® DataBlade® API Programmer's Guide describes information about the DataBlade API, the C-language application programming interface (API) provided with HCL Informix.
  - DataBlade® API Function Reference
    The Informix® DataBlade® API Function Reference describes the DataBlade API functions and the subset of Informix ESQL/C functions that the DataBlade API supports.
  - DataBlade® Developers Kit
    The DataBlade® Developers Kit (DBDK) guides contain information about the tools you can use to develop and package DataBlade modules, which extend the functionality of HCL Informix® databases.
  - J/Foundation Developer's Guide
    The J/Foundation Developer's Guide describes how to write user-defined routines (UDRs) in the Java™ programming language for Informix®.
  - R-Tree Index User's Guide
    The Informix® R-Tree Index User's Guide describes the HCL Informix R-tree secondary access method and how to access and use its components.
  - User-Defined Routines and Data Types Developer's Guide
    The Informix® User-Defined Routines and Data Types Developer's Guide describes how to define new data types and enable user-defined routines (UDRs) to extend HCL Informix.
  - Virtual-Table Interface Guide
    The 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.
    - Access methods
      This section describes access methods, explains why you create user-defined access methods, and shows you how to create user-defined access methods
    - Develop an access method
      These topics describe the steps that you take to implement a user-defined access method with the Virtual-Table Interface (VTI).
      - Choose features for the access method
        The Virtual-Table Interface (VTI) provides many optional features. Choose the features that you need to fulfill the access-method specifications.
      - Write purpose functions
        The Virtual-Table Interface (VTI) specifies the parameters and return values for a limited set of UDRs, called purpose functions, that correspond to one or more SQL statements.
      - Register purpose functions
        To register user-defined purpose functions with the database server, issue a CREATE FUNCTION statement for each one.
      - Register the access method
        The CREATE FUNCTION statement identifies a function as part of a database, but not necessarily as part of an access method. To register the access method, issue the CREATE PRIMARY ACCESS_METHOD statement, which sets values in the SYSAMS system catalog table.
      - Testing the access method
        To test the access method, take the same actions that users of the access method take to create and access virtual data.
      - Drop an access method
        To drop an access method, use the DROP ACCESS_METHOD statement.
      - Cannot rename databases that have virtual tables
        You cannot rename a database if the database has any tables that were created from the primary access method (also known as virtual table interface) or indexes that were created from the secondary access method (also known as virtual index interface).
    - Design decisions
      These topics present the choices that you make to optimize the performance and flexibility of the access method that you can create with the virtual-table interface (VTI).
    - Purpose-function reference
      These topics describe the purpose functions that the access-method developer provides.
    - Descriptor function reference
      These topics provide the syntax and usage for the functions that the HCL Informix® database server supplies to access-method developers.
    - SQL statements for access methods
      These topics describe the syntax and usage of the ALTER ACCESS_METHOD, CREATE PRIMARY ACCESS_METHOD, and DROP ACCESS_METHOD statements, which insert, change, or delete entries in the sysams system catalog table.
    - XA-compliant external data sources
      The HCL Informix® Transaction Manager recognizes XA-compliant external data sources, which can participate in two-phase commit transactions.
  - Virtual-Index Interface Guide
    The 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.

Develop an access method

These topics describe the steps that you take to implement a user-defined access method with the Virtual-Table Interface (VTI).

The following steps are a high-level summary of the steps that you take to provide an access method.

Choose the optional features that the access method supports.
Program and compile the C header files and purpose functions as well as the modules that the purpose functions call.
Execute the CREATE FUNCTION statement to register each purpose function in the sysprocedures system catalog table.
Execute the CREATE PRIMARY ACCESS_METHOD statement to register the user-defined access method in the sysams system catalog table.
Test the access method in an end-user environment.