public static void SerializeInventory()
        {
            var product = new Product
            {
                ProductID = 100,
                ProductName = "Product Thing",
                SupplierID = 10
            };

            var book = new BookProduct
            {
                ProductID = 101,
                ProductName = "How To Use Your New Product Thing",
                SupplierID = 10,
                ISBN = "1234567890"
            };

            Product[] products = { product, book };
            var inventory = new Inventory
            {
                InventoryItems = products
            };
       
            using (FileStream stream = File.Create(InventoryFileName))
            {
                var serializer = new XmlSerializer(typeof(Inventory), GetInventoryXmlAttributes());
                serializer.Serialize(stream, inventory);
            }
        }
        public static void SerializeProduct()
        {
            //new products object
            var product = new Product
            {
                ProductID = 200,
                CategoryID = 100,
                Discontinued = false,
                ProductName = "Serialize Objects",
                QuantityPerUnit = "6",
                ReorderLevel = 1,
                SupplierID = 1,
                UnitPrice = 1000,
                UnitsInStock = 10,
                UnitsOnOrder = 0
            };

            FileStream stream = File.OpenWrite(ProductFileName);
            using (TextWriter writer = new StreamWriter(stream))
            {
                XmlSerializer serializer = new XmlSerializer(typeof(Product));
                serializer.Serialize(writer, product);
            }           
        }