Hello tenbao,
Which version of SharePoint are you using? If you're in 2013 you can use the event receiver to sync your forms to DBXL. If you're in 2010, you could do a bulk upload/migration to dbxl and then reupload to SharePoint so that all your XML would hve the DBXL pi and DocID's.
Let me know and I can get more details.
Thanks!
Bre