Hello Shymaa,
PFB doc they give good insights.
http://scn.sap.com/docs/DOC-39944
http://scn.sap.com/docs/DOC-54468
http://scn.sap.com/docs/DOC-39944
http://scn.sap.com/docs/DOC-59759
http://scn.sap.com/docs/DOC-54469
I am travelling & responding from hand device. Please feel to give a call if incase some thing needs a discussion 
Thanks,
Kolusu