Welcome
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 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.
Programmer's Guide
The HCL® Informix® DataBlade® API Programmer's Guide describes information about the , the C-language application programming interface (API) provided with HCL Informix.
Database access
Exceptions and events
This section describes exceptions and events, and explains how to handle them in modules.
Event-handling mechanisms
An event-handling mechanism provides a way for one module to inform another module (or another part of the same module) that an event has occurred during execution of a function.
Invoke a callback
A callback function (or just callback) is a function that you write to handle a particular event.
Register a callback
For a callback to execute when its associated event occurs, you must register it with the mi_register_callback() function.
Callback handle
The mi_register_callback() function returns a callback handle, which accesses a registered callback within a module. A callback handle has the MI_CALLBACK_HANDLE data type.

HCL Informix® V15.0.0 documentation
Welcome to the documentation for HCL Informix® 15.0.0 and related client tools and products.
Product overview
HCL Informix® is a fast and scalable database server that manages traditional relational, object-relational, and dimensional databases. Its small footprint and self-managing capabilities are suited to embedded data-management solutions.
Installing
These topics describe how to install HCL Informix® database servers, client products, and modules.
Administering
In addition to administering the database server, you can tune performance, replicate data, and archive data.
Migrating and upgrading
You can upgrade to the 15.0.0 release of HCL Informix® or migrate from other database servers to Informix. Upgrading is an in-place migration method that uses your existing hardware and operating system software. Some changes to the Informix database server can affect upgrading from a previous release.
Client APIs and tools
You can use the HCL Informix® implementation of client APIs to develop applications for Informix database servers.
Embedding Informix®
When you embed HCL Informix®, you can use enterprise-class high-availability and high performance with embeddability features such as easy programmability, a small disk and memory footprint, and silent deployment.
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 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 modules
  These topics describe how to use built-in database extensions and separately installed 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.
  - Programmer's Guide
    The HCL® Informix® DataBlade® API Programmer's Guide describes information about the , the C-language application programming interface (API) provided with HCL Informix.
    - overview
    - Data manipulation
    - Database access
      - Connection handling
        This section describes how to initialize, establish, and close connections.
      - Execute SQL statements
        One basic task of a 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 modules.
        event types
        For a module, an event is a communication from HCL Informix® software that indicates the existence of some predefined condition, usually the occurrence of an exception (warning or error). The represents an event as one of the enumerated values of the MI_EVENT_TYPE data type.
        Event-handling mechanisms
        An event-handling mechanism provides a way for one module to inform another module (or another part of the same module) that an event has occurred during execution of a function.
        Invoke a callback
        A callback function (or just callback) is a function that you write to handle a particular event.
        Register a callback
        For a callback to execute when its associated event occurs, you must register it with the mi_register_callback() function.
        Types of callbacks
        The second argument of the mi_register_callback() function is the event type. The supports a type of callback for each event type.
        Connection descriptor
        The first argument of the mi_register_callback() function is a connection descriptor. This connection descriptor can be either a NULL-valued pointer or a pointer to a valid connection. The valid value depends on whether the calling module is a C user-defined routine (UDR) or a client LIBMI application.
        Callback-function pointer
        The third argument of the mi_register_callback() function is a callback-function pointer. The stores a pointer to the location of a callback function in the MI_CALLBACK_FUNC data type.
        Callback handle
        The mi_register_callback() function returns a callback handle, which accesses a registered callback within a module. A callback handle has the MI_CALLBACK_HANDLE data type.
        Registration duration
        Enable and disable a callback
        A callback must be enabled for the database server to invoke it. The mi_register_callback() function automatically enables the callback that it registers. You can explicitly disable a registered callback with the mi_disable_callback() function. When you disable a callback, you suspend its invocation. You can later explicitly re-enable it with the mi_enable_callback() function.
        Retrieving a callback function
        The mi_retrieve_callback() function returns a callback-function pointer (MI_CALLBACK_FUNC) when you pass in a callback handle (MI_CALLBACK_HANDLE). This function is useful when a module needs to change temporarily the callback that is registered for a particular event.
        Default behavior
        If no callback is registered for a particular event, the uses its default behavior when this event occurs. The default event handling depends on whether the event occurs in a C UDR or in a client LIBMI application.
        Callback functions
        To catch or handle an event, you create a C function called a callback function. In your module, you can register callback functions to handle recovery from events. The invokes a registered (and enabled) callback when the event associated with the callback occurs.
        Database server exceptions
        When the database server or a UDR raises a database server exception, the invokes any callbacks that are registered for the exception.
        State-transition events
        When the database server raises a state-transition event, the database server invokes any callbacks registered for the state transition. This section provides information about state-transition handling in modules, including an explanation of state-transition events and a description of how to handle a state-transition event in a C UDR and a client LIBMI application.
        Client LIBMI errors
        The throws the MI_Client_Library_Error event to indicate an error in the client LIBMI library.
      - XA-compliant external data sources
    - Create user-defined routines
    - Appendix
      This section contains additional reference information.
  - Function Reference
    The IBM® Informix® DataBlade® API Function Reference describes the functions and the subset of functions that the supports.
  - Developers Kit
    The Developers Kit (DBDK) guides contain information about the tools you can use to develop and package modules, which extend the functionality of HCL Informix® databases.
  - J/Foundation Developer's Guide
    The HCL® 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 HCL® 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 HCL® 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 IBM® 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 IBM® 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 module.
Data warehousing
In addition to designing and implementing Informix® dimensional databases, you can use tools to create data warehouse applications and optimize your data warehouse queries.
Designing databases
The first step in creating a relational database is to construct a data model, which is a precise, complete definition of the data you want to store. After you prepare your data model, you must implement it as a database and tables. To implement your data model, you first select a data type for each column and then you create a database and tables and populate the tables with data. You can also implement fragmentation strategies and control access to your data.
JSON compatibility
You can use the popular JSON-oriented query language created by MongoDB to interact with data stored in HCL Informix®.
Security
You can secure your Informix® database server and the data that is stored in your Informix databases. You can encrypt data, secure connections, control user privileges and access, and audit data security.
SQL programming
You can use the HCL Informix® implementation of the SQL language to develop applications for Informix database servers.
Troubleshooting HCL Informix®
Several troubleshooting techniques, tools, and resources are available for resolving problems that you encounter in your HCL Informix® database server environment.

Callback handle

The mi_register_callback() function returns a callback handle, which accesses a registered callback within a module. A callback handle has the MI_CALLBACK_HANDLE data type.

Use a callback handle to identify a callback for the following tasks.


Callback task	function
Enable a callback	mi_enable_callback()
Disable a callback	mi_disable_callback()
Retrieve a pointer to a callback function	mi_retrieve_callback()
Unregister a callback	mi_unregister_callback()

Tip: The last argument of the mi_register_callback() function is also a callback handle, but this argument is reserved for future use and must currently be a NULL-valued pointer.