Hi Nafiz, 

the EXPORT command exports the whole database, hence for the example code below:
a file path/to/export.xml would be created on the machine running BaseX, with the serialized results of your database.

Hope this helped clear things up :)
Kind Regards
Michael
Am 02.02.2012 um 16:05 schrieb Nafiz Al Naharul Islam Grameenphone IT Ltd.:

$session->execute('OPEN myDB; EXPORT path/to/export.xml;CLOSE myDB;')

Command is not clear to me and where I'll place my xquery ?

But the second one is perfect and its working with xquery.