<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="DAL" value="FactoryInterface.Oracle"/>
  </appSettings>
</configuration>

namespace FactoryInterface
{
    interface IDAL
    {
        void insert();
    }
}

namespace FactoryInterface
{
    class Program
    {
        static void Main(string[] args)
        {

            string config = System.Configuration.ConfigurationManager.AppSettings["DAL"];
            Console.WriteLine(config);
            Type t = Type.GetType(config);
            IDAL dal =(IDAL) System.Activator.CreateInstance(t);
            dal.insert();
            Console.ReadKey();

        }

    }
    class MySql : IDAL {
        public void insert() {
            Console.WriteLine("this data insert by MySql");
        }
    }
    class Oracle : IDAL
    {
        public void insert()
        {
            Console.WriteLine("this data insert by Oracle");
        }
    }
}