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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.
DataBlade® API Programmer's GuideThe 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
Develop a user-defined routineA 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.
Designing a UDRThis section provides the following design considerations for the development of a C UDR: development tools, uses of a UDR, portability, and insert and update operations.
Uses of a C UDR

Uses of a C UDR

The following table summarizes the tasks that a C UDR can perform. It also describes where you can find additional information for each of these UDR uses.


Type of UDR	Purpose	More information
Cast function	A UDR that converts one data type to another	Write a cast function
Cost function	A UDR that determines the cost of execution for an expensive UDR	Write selectivity and cost functions
End-user routine	A UDR that performs some common task for an end user	Write an end-user routine
Iterator function	A function that returns more than one row of data	Write an iterator function
Opaque-type support function	One of a group of user-defined functions that tell the database server how to handle the data of an opaque data type	Create an Opaque Data Type
Operator-class function	User-defined functions that define operators to use with a particular secondary access method	See your access-method documentation.
Negator function	A user-defined function that calculates the Boolean NOT operation for a particular operator or function.	implementing a negator function with a C user-defined function
Selectivity function	A UDR that determines the percentage of rows likely to be returned by an expensive UDR	Write selectivity and cost functions
Parallelizable UDR	A UDR that can run in parallel when executed within a PDQ statement	Creating parallelizable UDRs
User-defined aggregate	A function that calculates an aggregate value on a particular column or value	Write an aggregate function

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