Extension Methods, DataSet & DataReader

Extension methods help you to "add" methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type. Extension methods are a special kind of static method.

For example, let us assume Car.dll is the 3rd party DLL and source is not available.
Car Class Library - Details.CS

namespace Car
{
    public class Details
    {
        public string Wheel(string cartype)
        {
            if (cartype=="CORROLA")
                return "Two";
            if (cartype == "JEEP")
                return "Four";
            else
                return "No Wheel";
        }
    }
}