Here is the proper order for the CORBA development process:

1. Write the IDL that describes the interfaces
2. Run the IDL pre-processor
3. Develop the CORBA server and the CORBA client
4. Compile and run the CORBA server
5. Compile and run the CORBA client

If the concept of the Object Request Broker is one cornerstone of the CORBA architecture, the Interface Definition Language (IDL) is the other. IDL, as its name suggests, is the language used to define interfaces between application components. Note that IDL is not a procedural language; it can define only interfaces, not implementations. C++ programmers can think of IDL definitions as analogous to header files for classes; a header file typically does not contain any implementation of a class but rather describes that class's interface. Java programmers might liken IDL definitions to definitions of Java interfaces; again, only the interface is described and no implementation is provided.
New Term: The Interface Definition Language (IDL) is a standard language used to define the interfaces used by CORBA objects.
The IDL specification is responsible for ensuring that data is properly exchanged between dissimilar languages. For example, the IDL long type is a 32-bit signed integer quantity, which can map to a C++ long (depending on the platform) or to a Java int. It is the responsibility of the IDL specification and the IDL compilers that implement it, and to define such data types in a language-independent way.