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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.
Create user-defined routines
Extend data types
This section describes the ways to extend data types with C user-defined routines (UDRs).
Create an Opaque Data Type
This section describes how to design and write an opaque data type.
Write opaque-type support functions
The database server does not know the internal representation of an opaque type. To handle the internal representation, you write opaque-type support functions. These support functions tell the database server how to interact with the opaque type.
Stream support functions

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
    - Create user-defined routines
      - Develop a user-defined routine
        A C user-defined routine (UDR) is a UDR that is written in the C language and uses the server-side implementation of the DataBlade® API to communicate with the database server. C UDRs (functions and procedures) are implemented as C-language functions. DataBlade modules often include C UDRs that are made available for use by registering them in the database.
      - Write a user-defined routine
        This section outlines some implementation issues for C user-defined routines (UDRs). This section also describes the specific features and tasks of a C UDR.
      - Manage memory
        A C user-defined routine (UDR) has access to shared memory for dynamic allocations and stack memory for routine arguments (including the MI_FPARAM structure), local stack variables, and return values.
      - Create special-purpose UDRs
        This section describes how to create special UDRs, such as iterator functions, user-defined aggregates, and optimization functions.
      - Extend data types
        This section describes the ways to extend data types with C user-defined routines (UDRs).
        Create an Opaque Data Type
        This section describes how to design and write an opaque data type.
        Design an opaque data type
        Write opaque-type support functions
        The database server does not know the internal representation of an opaque type. To handle the internal representation, you write opaque-type support functions. These support functions tell the database server how to interact with the opaque type.
        Support functions as casts
        Stream support functions
        The streamwrite() support function
        On a destination database server, the streamwrite() support function converts opaque-type data from its binary representation to its stream representation.
        The streamread() support function
        On a target database server, the streamread() support function converts opaque-type data from its stream representation to its binary representation, which is stored in the target database.
        Convert opaque-type data between stream and binary representations
        The DataBlade® API provides several functions to convert built-in data types between binary and stream representations. The streamwrite() and streamread() support functions can use these DataBlade API functions to convert a UDT between its binary representation and its stream representation.
        Disk-storage support functions
        Handling locale-specific opaque-type data (GLS)
        Registering an opaque data type
        This section explains how to register an opaque data type.
        Provide statistics data for a column
        The database server can provide statistics data for the columns of a table. This statistics data describes the distribution of the values within a column. The query optimizer uses this statistics data to determine the best path for an SQL statement. With this information, the optimizer can estimate the effect of a WHERE clause by examining, for each column included in the WHERE clause, the proportionate occurrence of data values contained in the column.
        Optimize queries
    - 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.

Stream support functions

The following support functions convert a UDT to or from a stream representation while reading the UDT from a stream or writing the UDT to a stream.

streamwrite(): Conversion of opaque-type data from its binary representation to its stream representation
streamread(): Conversion of opaque-type data from its stream representation to its binary representation

The stream representation is self-contained and includes enough information to enable the streamread() function to recreate the UDT instance.

Important: If the UDT includes out-of-row data, the stream representation normally includes that data.

Enterprise Replication invokes the streamwrite() and streamread() support functions when replicating UDT columns. The streams it passes to these functions are Enterprise Replication streams, a write-only stream for streamwrite() and a read-only stream for streamread(). You cannot open or close an Enterprise Replication stream or use the mi_stream_setpos() or mi_stream_seek() function on it. For more information about Enterprise Replication, see the HCL® Informix® Enterprise Replication Guide.

Important: If a column that includes out-of-row data is to be replicated, avoid placing a NOT NULL constraint on the column. Enterprise Replication collects out-of-row data for transmission after the user transaction has committed. Due to activity on the replicated row, the data might not exist at the time Enterprise Replication collects it for replication. In such cases, Enterprise Replication normally applies a NULL on the target system.