Data Contract Inside another data contract

Hi Team,

Can you please help me in knowing the way to write a data contract inside another data contract as i want to build a custom service xml schema with sub xml elements. As per my knowledge i need to write the contract in the parm methods of another data contract but not sure how to write. Can you please help me in knowing it.

<?xml version="1.0"?>
<LoginResponse>
<SessionId>987</SessionId>
<EmailId>testing@gmail.com</EmailId>
<Authentication>
<ResponseCode>1</ResponseCode>
<ReasonCode>10</ReasonCode>
<ReasonDescription>Not Valid</ReasonDescription>
</Authentication>

</LoginResponse>

Regards

Venky