The answer to "how do I get from the DataSet to the response" is, "however
you want to".

The best way will not only depend on some abstract "best practices", but
also on you and your areas of expertise. For instance, if you're good with
XSL, you might want to use a stylesheet to transform the XML of the DataSet
into the correct form for the response. If not, you may simply be better off
copying the data from the DataSet into the proxy objects for the response:

// Proxy classes:

public class Employee
{
   public string FirstName ...;
   public string LastName ...;
   public int ID ...;
}

public class Response
{
   public int NumberOfEmployees;
   public Employee[] Employees;
}

[WebService]
public class MyService : WebService
{
   [WebMethod]
   public Response MyMethod(Request request)
   {
       DataSet ds = GetDataSet(request);
       DataTable employeesTable = ds.Tables["Employees"];
       Response response = new Response();
       response.NumberOfEmployees = employeesTable.Rows.Count;
       response.Employees = new Employee[response.NumberOfEmployees];

       for (int i=0; i<employeesTable.Rows.Count; i++)
       {
           DataRow dr = employeesTable.Rows[i];
           Employee employee = new Employee();
           employee.FirstName = (string) dr["FirstName"];
           employee.LastName = (string) dr["LastName"];
           employee.ID = (int) dr["ID"];
           response.Employees[i] = employee;
       }

       return response;
   }
}

Of course, if your requirements are not this simple, then your solution will
not be this simple, either.

John

you didnt say in your original post that you need it in a specific format