How to recover a deleted document in Jackrabbit?

[Xiaojie Shen]

Hello
It seems files are still maintained in datastore after they are deleted. Are 
version indexes also maintained?
How are the files under 
/jackrabbit-webapp_default/server/default/jcr:root/jcr:system/jcr:versionStorage/...
 related to the document storage?
It is hard to get a clue from the coded file storage structure. How can 
administrator recover a deleted document?
Thanks in advance!
Shen