i have some more doubts. in this tutorial 
http://www.ros.org/wiki/ROS/Tutorials/UnderstandingServicesParams
UnderstandingServicesParams 
 what is a namespace. and where is copy stored. is it stored in some file?

this is what given in tutorial
"You can even load these yaml files into new namespaces, e.g. copy:

$ rosparam load params.yaml copy
$ rosparam get copy/background_b
255 "

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