Loading a mod question

I have created a few mods I would like to try. I have gone through the mod doc in detail, and I understand how to mod, and I believe I understand the modding folder structure. I modified 4 xml files (custom planets, starbases, planetary improvments, and techs) and placed them in the mods/default/data/* that corresponds to the particular mod. I set the mods folder to the default in options. I am not getting the mods in the game. What else do I need to do to have these 4 files used as mods? Is there some key file that needs to go with the mod'd files in the mod folder?