Why to use [Datacontract] and [DataMember] WCF? - wcf

Question

Supposing that we have the following code for WCF service and a database with an Employee table.
Why use [DataContract] and what are benefits of using all [DataMember] ?
We can use all Employee details without using [DataContract].
[ServiceContract]
public interface IEmployeeService
{
[OperationContract]
Employee GetEmployeeDetails(int EmpId);
}
[DataContract]
public class Employee
{
private string m_Name;
private int m_Age;
private int m_Salary;
[DataMember]
public string Name
{
get { return m_Name; }
set { m_Name = value; }
}
[DataMember]
public int Age
{
get { return m_Age; }
set { m_Age = value; }
}
[DataMember]
public int Salary
{
get { return m_Salary; }
set { m_Salary = value; }
}
}
Implementatin of Service:
public class EmployeeService : IEmployeeService
{
public Employee GetEmployeeDetails(int empId)
{
Employee empDetail = new Employee();
return empDetail;
}
}
And our Client:
private void btnGetDetails_Click(object sender, EventArgs e)
{
EmployeeServiceClient objEmployeeClient = new EmployeeServiceClient();
Employee empDetails;
empDetails = objEmployeeClient.GetEmployeeDetails(empId);
}