Looking for a schema document

I am new to Opencart 1.5.6 customization and am looking at making a custom Product feed for Google and Amazon.

But... I dont know all the field names and such. Is there a document with all the default field names for the Opencart schema?

Any help is appreciated

Jon Black
Hawk Services
www.hawkswing.com
jabhawk1@gmail.com

here is at least something:
http://forum.opencart.com/viewtopic.php?f=24&t=21748

check here to may find more:
http://forum.opencart.com/viewforum.php?f=24

I did it, so far, the hard way...
Ernie