What are you trying to achieve? Assuming you are using CMS 6 upwards then you can use the DDS to grab xform data directly (OK but you do need the form id). Linus Ekström put a good post about this together a while back:
Is it possible to get XForm data with just the form data ID, or do you have to have the form ID too?
However, it's marked as deprecated and always returns NULL. If you pass in the form ID to the overload, it works fine.
If I just have the form data ID (not the form ID), can I load the data?