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# 3.1 Defining the Interface in OMG IDL

The first step in developing a CORBA system is to define the interface(s) in OMG IDL. In the ``Hello World'' example, this is trivial as we have a single interface containing a single operation. However, it is worth noting the use of the `#pragma prefix` directive, and the definition of the `HelloWorld` module to contain our interface. These mechanisms ensure that we do not pollute the global namespace and should be adopted by every good CORBA citizen! The IDL shown below can be found in the file
```Fnorb/examples/hello-world/HelloWorld.idl`''.

    #pragma prefix "dstc.edu.au"

    //
    // "Hello World" example!
    //
    module HelloWorld {

        const string Message = "Hello CORBA World!";

        interface HelloWorldIF {
            //
            // The IDL version of the old faithful, 'Hello World' example!
            //
            // This operation takes no parameters and returns a string.
            //
            string hello_world();
        };
    };