How to extend product export functinality

Hi All, I am writing some module and want to extend the product export functionality of oxid. I want to add some more coulmns to the export. When I go to product export check the html though firebug, I can see the hidden field referring the genexport_do class and function start();
I have written my own class which extends the genexport_do class. In my class I just call the start function of my parent class. But nothing happens when I call my class. It creates a file in export folder but with 0 KB size. My class looks like


class froomerce_generateFeed extends GenExport_Do
{
    public function start()
    {
        parent::start();
        
    }
}

First I want to ask can I do this? if Yes how can I add some more columns to simple product export ? Are other some other files in which I have to do some thing?

Regards,
Awais Qarni