ASP.NET 3.5 Enterprise Application Development with Visual Studio® 2008: Problem - Design - Solution

1.3. Solution

As stated earlier, this solution uses a three-layered architecture: the user interface (UI), the business logic layer (BLL), and the data access layer (DAL). When building a solution in Visual Studio, you can include multiple project types in the same solution, making it easy to manage all three layers in one place. The UI layer consists of a web application and server-side controls. Essentially, anything that the user interacts with directly is considered part of the UI layer. UI developers or designers control the overall look and feel of the site, and typically excel at design, rather than programming. They focus on fonts, colors, and making sure the application meets the company's branding requirements.

The BLL contains all the business and validation rules that are the real "brains" of the application. For example, suppose you have a screen that allows the user to create a user in the system. The user's name is required and must be unique when adding a new user. You could put logic in the web form that enforces these two rules. Now suppose a new requirement comes along: The application must import a comma-separated file of user names. The user name is still required and must be unique, so that logic would have to be duplicated in the import logic. If you were to put the logic in a class, then the web form and the import program could call the same code. Anytime new rules are added to the application, you would simply change the logic in the shared class. This ...