I want to know how to get and set the xml string data to DataSet object in

Currently, I am working on an application that I need to retrive data from
Database and convert the data of the DataSet to a xml string. And them, the
xml string data will pass to the web client. After the web client obtain
the xml string, it need to convert back to DataSet.

Would anyone can tell me to how to convert the Dataset data to a xml string
and how to convert the xml string data back to the Dataset?