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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.
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.
Database access
Connection handling
This section describes how to initialize, establish, and close connections.
Initialize the DataBlade® API
Before you can use the DataBlade® API to communicate with the database server, you must make sure that it is initialized.

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 overview
    - Data manipulation
    - Database access
      - Connection handling
        This section describes how to initialize, establish, and close connections.
        Session management
        Session management is the handling of a connection to a database server and the associated session within a DataBlade® API module. A session is the period of time that elapses between when a client application establishes a connection and when this connection is closed.
        Initializing a client connection
        Before a client LIBMI application can establish a connection, it must initialize the connection with the name of the database server and database to which it needs to connect.
        Establish a connection
        The DataBlade® API functions, mi_open() and mi_server_connect() (client only), are constructor functions for a connection descriptor.
        Associate user data with a connection
        The connection descriptor provides information about various data type structures associated with the current connection. In addition, you can store the address of private information, called user data, in the connection descriptor. The connection descriptor can hold this user-data pointer, which points to the private user-data information.
        Initialize the DataBlade® API
        Before you can use the DataBlade® API to communicate with the database server, you must make sure that it is initialized.
        Close a connection
        To close a connection, free the associated connection descriptor.
      - Execute SQL statements
        One basic task of a DataBlade® API module is to send SQL statements to the database server for execution.
      - Execute user-defined routines
        This section provides information about how to call a user-defined routine (UDR).
      - Exceptions and events
        This section describes exceptions and events, and explains how to handle them in DataBlade® API modules.
      - XA-compliant external data sources
    - Create user-defined routines
    - Appendix
      This section contains additional reference information.
  - 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.
  - 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.

Initialize the DataBlade® API

Before you can use the DataBlade® API to communicate with the database server, you must make sure that it is initialized.

When you establish a connection, the DataBlade® API function automatically initializes the DataBlade® API. However, if your DataBlade® API module does not establish a connection, it must still ensure that it initializes the DataBlade® API.

Important: If the DataBlade® API was not initialized, calls to subsequent DataBlade® API functions generate errors.

The following table lists the functions that can initialize the DataBlade® API.

Table 1. DataBlade® API functions that initialize the DataBlade® API
DataBlade® API initialization function	Valid in client LIBMI application?	Valid in user-defined routine?
mi_client_locale()	Yes	Yes
mi_get_default_connection_info()	Yes	Yes
mi_get_default_database_info()	Yes	Yes
mi_get_next_sysname()	Yes	No
mi_get_parameter_info()	Yes	Yes
mi_init_library()	Yes	No
mi_open()	Yes	Yes
mi_register_callback()	Yes	Yes
mi_server_connect()	Yes	No
mi_set_default_connection_info()	Yes	Ignored
mi_set_default_database_info()	Yes	Ignored
mi_set_parameter_info()	Yes	No
mi_sysname()	Yes	Yes

One of the functions listed in the preceding table must be the first DataBlade® API function called in a DataBlade® API session. If you do not call one of these functions, the DataBlade® API is not initialized and all subsequent DataBlade® API calls return error status.