Vimalkumar,
But if you have the persistence API do that, Orbeon Forms won't be able to read the data back for further editing. If you want to have this happen, I'd do it independently from the persistence API, with a button in your form (which could be the "Save" button, if you'd like), that as, part of a process, calls the send() action doing a POST to your XQuery in eXist that appends the data somewhere. Would this make sense?
http://doc.orbeon.com/form-runner/advanced/buttons-and-processes/index.htmlAlex
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