design of LVM2

i started working on LVM2 code few days ago. i was browsing through code to understand basic architecture and command flow, but couldn't get it exactly. i could manage to understand communication between LVM and device-mapper but still have lot of doubts in mind and i am not feeling very comfortable to put all of them here. So are there any design-documents available to understand LVM2. It will be great help to me. Thanking in advance.