Web Service via Data Access Object Pattern

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using AndrewGolik.DaoTraining.DataAccessLayer;
using System.Data.SqlClient;

namespace AndrewGolik.DaoTraining.DataAccessLayer.MSSql
{

    public class MSSqlDaoFactory:DaoFactory
    {

        

        public static string ConnectionString
        {
            get
            {
                if (ConfigurationManager.ConnectionStrings["MsSqlDao"] == null)
                    throw new NullReferenceException("MsSqlDao connectionString configuration is missing from your web.config.");
                string connectionString = ConfigurationManager.ConnectionStrings["MsSqlDao"].ConnectionString;
                if (String.IsNullOrEmpty(connectionString))
                    throw new NullReferenceException("MsSqlDao connectionString configuration is missing from your web.config.");
                else
                    return connectionString;
            }
               
            
        }
        public override CustomerDao GetCustomerDao() 
        {

           return new MSSqlCustomerDao();
            
        }

        public override OrderDao GetOrderDao() 
        {

            return new MSSqlOrderDao();
        }

     


    }

}