As mentioned, tiered development is implemented in Microsoft .NET by using an assembly. An assembly is analogous to a component in Microsoft's previous development platforms. An assembly contains objects and methods and compiles to a DLL. The assembly can be referenced and used by your Web or Windows form.
In the next few sections, you're going to see how to implement an additional tier in some of the examples from Hour 11, specifically the product list screen and the product details screen. The original examples are not provided in this chapter, so now might be a good time to go back and review the purpose and implementation of these screens in Hour 11.
As you recall, the product list screen displayed a list of all products in the Northwind database and the product details screen displayed detailed product information for a single product. As mentioned earlier, all data access and business logic (if any) will be removed from the Web forms and placed into an assembly. The Web forms will then call the assembly to get data, rather than directly calling the database itself.